I always play full parties, because I enjoy playing with my loot to much, and the consensus seems to be that a full party will not hit XP cap by the end of ToB, so I'm wondering how much XP a determined party might with, without exploiting infinite XP battles/rest-respawns. For instance, I have no interest in fighting mephits from the infinite respawn portals of Irenicus dungeon until I hit 8,000,000xp ;~)
I think the key observation is that certain properties of the game are keyed off the main char's level - not their xp, but their highest character level. If you hit 11 in Irenicus dungeon before recruiting Minsc (quite possible for Druid or Thief) then he will start with a whopping 1.2M xp - that is quite a start there! Careful selection of characters (Aerie, Anomen, not sure which others) will also gain a significant bonus, while others (Neera, Rasaad) will languish close to the BG1 xp cap, so picking the right party early seems important.
The second idea is that, to some extent, the game scales according to PC level, so hitting high level early will give more difficult encounters with higher XP. The best way to boost XP for the party quickly is to take the mainline quest, where large fixed awards will have you power leveling in no time.
The final observation is to note that thieves get progressively more XP for picking locks/removing traps every 5 levels, so defer as many traps and locks as possible until the thief is getting at least 950/2750 xp per lock/trap. This means running Jan, yoshi or Hexxat as your thief, as Nalia/Imoen will never hit those levels, or playing the thief yourself, which comes full circle to point 1.
So my plan is to play a primary thief, probably a swashbuckler, and speed down the mainline quest. Contemplating dualing into fighter or cleric after getting use any item around 3,000,000 xp, which is character level 24. I should hit this before the end of SoA, which should hopefully mean max scaling for SoA though (this is above the original game's level cap) but not sure if I miss out on further scaling in ToB. Dualing to mage is also tempting, as I then have a legitimate excuse to scribe many more scrolls (erase/scribe churn is also out as an exploit) The trouble here is that I can never hit 25 and reclaim the thief levels, so optimistically assuming I would hit the xp cap, the highest I can dual(to mage) is 22.
So my first curiosity is whether anyone can hit XP cap. If so, the two measures of success are how many chars can hit the XP cap, and how much XP the lowest-xp character can obtain. Any predictions?
(note that I am still some way off starting this run - I will need to play a thief all the way through BG1, and have a few other play throughs queued up, but bouncing thoughts for play throughs will help me pick which happens next