My players have run up against time and speed limits. The dungeon portal only stays open for up to six hours, and they've started running up hard against this time limit during their last couple of expeditions. This has severely limited their ability to explore outside of their currently-mapped area. Most of my players seem to be in favor of setting up a safe zone and camping in the dungeon, but one of them was asking me about the encumbrance rules yesterday and talking about doing a low-gear, evasive reconnaissance operation one week, and then sending a more heavily-armored follow-up expedition to selected targets the next week.
I think this is a very interesting idea. I hesitate to call it a good idea, because I've never seen it done before, but it's very much in the style of "dungoneering as heist movie, not action movie", and I think it'd probably work well if done cleverly.
So let's think about this a bit.
To move 120' per turn, you need to be carrying less than 5 stone. 90' requires less than 7 stone, and 60' requires less than 10 stone. An unarmored wardog has a speed of 150', while an armored wardog has a speed of 90', and a mule can carry up to 20 stone at 120', but drops to 60' above that.
There are a couple of proficiencies which might be unusually good for this type of operation. Endurance lets you skip rest turns, increasing your effective movement speed by 20% (although notably, skipping multiple rest turns doesn't seem to stack up increasing penalties under rules as written). Running boosts your base movement speed by 30' in chainmail or lighter armor. Skirmishing lets you disengage without pre-declaring it (I'm not sure this is actually good if your doctrine is evasive, though, because in that case you probably tend to declare disengage?).
Dexterity really shines as a stat in this type of party composition, because it lets you get your AC up into the 7-8 range without having to compromise your speed with heavy armor.
In terms of party composition:
Wizards, thieves, bladedancers, bards, and nightblades are not inconvenienced in the least by requirements for reduced gear, and can all easily maintain 120' speed.
Barbarians, explorers, and other classes limited to chainmail might have to make some sacrifices to maintain 120' speed. I think our current explorer is in chainmail with an arbalest and a spear, which is 6 stone of gear for 90' speed. To hit 120' with a real ranged weapon, she'd probably have to downgrade chainmail to ringmail and spear to sword. But 90' might be an acceptable movement speed; it's still 50% faster than our party's current speed, and at 90' you can use armored wardogs.
Assassins are already a weird case, because they can use heavy armor, but they lose a lot of their abilities if they do. For 120' speed, leather, a polearm, and a ranged weapon is probably a good bet. At 90', they have more options.
Assassins and explorers are both notable because they have Dex as a prime req (so they can boost it during character creation), and they get fighter damage bonus. In a high-speed low-drag party, they're both good front-line options.
Thrown weapons might actually be decent in this paradigm; each javelin is an item rather than a stone, so you can fill out your last couple items of encumbrance with them (say you're an explorer going for 120' speed in chainmail with a sword; that puts you are 4 stone and one item. You can still carry four javelins or oil flasks, which put you at 4 stone and 5 items, one short of 5 stone and 90' speed). Slings are also substantially less horrible here than usual, because they have decent range (more than double that of javelins) and only weigh one item of encumbrance with their ammunition. d4 damage sucks, but fighter damage bonus, Inspire Courage, and Bless all apply...
Fighters, clerics, dwarves, and spellswords all have some difficulty at high speeds. To hit 90' speed, you have to lose any two of plate, shield, and spear. Best possible AC without magic or dexterity at 90' is 7, via banded mail, shield with fighting style, and a sword (and four flasks of oil or javelins). It goes without saying that the weight-reduction effect of magic armor is fantastically good in this context. Plate with a one-handed sword used in both hands is not a terrible choice if you don't have FS:Shield (as if), and banded+spear (or polearm) is probably doctrinal for second-liners (including spellswords). At 120' speed, all of these classes are going to have real trouble without magic armor. Fighters do get more proficiencies than most classes, and for one specializing in this sort of thing Running is actually a pretty strong option. Chainmail armor, shield with fighting style, and a spear weighs 6 stone, which would normally put you at 90', but Running boosts that back up to 120' with AC6.
Thrassians and ratmen, unfortunately, are in a whole 'nother level of trouble, since their base movement speed is only 60'. Besides Running, their best option is probably to ride mules. We've previously ruled that an adult human weighs about 15 stone. Since mules can carry 20 stone at 120', a thrassian gladiator in chain (19st total) could ride one at 120', and then dismount to fight with tooth and claw at AC7. This poses some difficulties, as mules can be killed and you need to remount if the party decides to retreat, but Riding as a proficiency scales well into the late game and solves the more pressing of those two problems (I am not so cruel a DM as to rule that Riding (Mules) should be separate from Riding (Horses)). The other can be solved by bringing more mules, which you were going to want to do anyway for mundane adventuring gear and hauling treasure; if you're not going to need a piece of gear close-to-hand in combat, put it on a mule.
So with all that said, I think 90' speed is very doable. Three of the five PCs transition very well to lightweight play (mage, bladedancer, and explorer). The elven enchanter and bard henchmen do as well. The fighter henchmen are mostly either expendable or replaceable with wardogs (of which the party already has two). The five characters who run into difficulties are Scarth's two cleric henchmen, Clarence the dwarf, Chathis the lizardman, and Dogeater the ratman. Clarence runs plate and two-handed warpick, but could hit 90' by switching to a one-handed pick used in both hands. Slagathor the Cleric runs plate and polearm with Martial Training, and could drop down to banded and polearm. I think Rheingold is plate+shield with Lay on Hands; dropping the shield is probably the best option for him. Dogeater and Chathis really don't have many options besides being mule-dragoons.
Anyway, I'm excited about this proposed alternate style of play and hope it happens. I've been a little bit bored with the dungeoneering game recently, and mixing it up would be good.