If we assume that ordinary individuals are 1st and 2nd level, then we are dealing with in a 20th level fighter someone that could face 300+ opponents in melee combat and defeat them handedly. We are dealing with someone who can fall from tall places reach terminal velocity and for whatever reason (destiny, superhuman toughness, luck, whatever hit points represent) and not be in mortal peril. We are dealing with someone that can easily and reutinely defeat a dozen well trained armed individuals with his bare hands.
How much XP does 4 years of college get you, for example.
By the book, absolutely none. Since this answer doesn't reflect our experience, it probably reasonable to suggest that there are ways of obtaining XP which are not reflected in the rules because they don't reutinely come up in play. For example, training. Simulated challenges overcome are still challenges overcome. They may not grant you XP at anything like a rate that would profit adventurers compared to killing things and taking thier stuff, but they are probably out there.
The question of how much XP you obtain for training of a particular intensity is an interesting one, but since we've no widely accepted rules, it won't really help us answer what level Einstein was. A better approach is the pair of questions: "Is there anything Einstein did that the suggested character cannot do?" and "Is there anything that the suggested character can do that Einstein cannot?"
In the case of Einstein, I believe that my suggestion reflects Einstein about as well as the D&D rules can. A +22 bonus to a Knowledge skill means that you can sit down with a paper and pencil, 'take 10' and answer even the hardest and most obscure questions about that field of knowledge (DC 30). By taking 20, Einstein could answer questions of DC 42, which is a reasonable DC for hard problems for which no one has the answer too. But this is hardly the hardest problem that Einstein can answer. By taking 20, with the aid of an assistant such as his wife (+2 bonus from 'Aid Other'), books and journals in physics (+2 bonus from masterwork physics kit) or a lab, and other means of obtaining bonuses, the suggested 'Einstein' can answer questions approaching DC 50. I have no problem believing that solving even the most sophisticated problems can be considered to be succeeding in a series of smaller DC 50 challenges.
I would go further than that. My Einstein plays the violin (usually badly), has a reasonable amount of time invested in skills he's picked up from doing all the things that he does when he's not doing physics - like working as a patent clerk, for example. And he still has enough skill points for all of that, even as a 'lowly' 8th level character. So no, within the limits of the rules, there is nothing that Einstein could do that the suggested character couldn't do, and furthermore there is very little that the suggested character could do that Einstien couldn't do. The suggested character is somewhat better in combat than I would be perfectly happy with, but neither is that character a match for any sort of trained martial character.
But, back to the question of how much XP you get from 4 years of college, since such a question can tell you what level ordinary people are. If it is reasonable to assume that ordinary people are commonly higher than 8th level, then its unreasonable to assume that extraordinary people are only 8th level.
However, I think it is perfectly reasonable to assume that ordinary people are less than 8th level.
Imagine that normal training amounts to 1 XP per day, and can generally begin whenever someone obtains maturity (and they become full fledged 1st level characters, and not merely 0th level apprentices). Imagine further that studious people don't waste their time and can manage to perform work which is beneficial to thier education 300 days a year. So, in 10 years time they might obtain a PhD (and perhaps a bit of post-doc experience), and they would be 3rd level experts with about 3000 XP. At that point, the hypothetical theoretical physicist might have a +12 bonus in his chosen field, capable of taking 10 and answer ordinary tough physics questions (DC 20) of the sort we'd only expect experts to know at will, and when taking 20 answering some of the hardest questions in the character's chosen field (DC 30) of the sort that only experts can even pose. Of course, most people don't daily do things that improve thier abilities, and most people aren't so studious as to push themselves 300 days a year, so few people actually become so skilled. Extremely talented physicists with the highest commitment to thier work might with the best training obtain 5th level or so before thier mental faculties and energy begin to fade, and such keen powers of perception and problem solving might earn them the universal recognition of thier peers.
