I am curious what level (or XP total) you would expect to beat the game with under these conditions:
1. Solo: You play through the entire game with just one character
2. Low%: You avoid doing any quests or exploring any areas with the exception of those that are mandatory to beat the game

I note that there are a few variables that might affect this:
1. Whether you use glitches (like polymorph teleporting) to skip parts of the game (in BG2, most of Chapter 4 can be skipped this way, for example)
2. In BG2, which route you take through Chapter 3.
3. Which game you are playing in the first place (BG2 gives a lot more experience than BG1)
4. In BG2, whether or not you are playing a thief (extra XP from traps) or a mage (extra XP from scrolls)

Also, has anyone actually done solo low%?

Well, in BG1 if you stick strickly to mandatory quests, so I'm not going to include XP for anything else, including monsters, you can boil it down to this:

Nashkel Mines == 650
Bandit Camp == 3750
Cloakwood Mines == 6000
Seven Suns == 7000
Sewers == 2000, 2500 or 3000
Iron Throne == 2000
Candlekeep == 4950
Iron Throne (assassination) == 5450
Sarevok == 31800

So that means a minimum of 63600 XP. That means a Fighter, Paladin, Ranger could get to level 6. A Thief, Mage, Bard, Cleric could get to level 7. A Druid could get to level 8.

Of course, in reality things would never work that way. Also, this was not scientific: I just included the end XP for each stage.