I emphasised that I wasn't sure if it kept because as far as I could tell there was no difference in the total xp gains over a whole game between my Good Learner and regular chars. This is very difficult to compare directly, of course, but I would have thought a 40% difference would be way more noticeable. I don't think anyone's gone to the effort to check.
I must agree with those that say the difference in actual levels is very small. Only over the first 10 levels will you notice a big difference in all these xp bonus factors. After that the xp differences between levels are so big that they don't make much difference, and it's only the slow troll levelling that's particularly noticeable. Later in the game it's mostly bosses that provide the vast wealth of xp, and as gut says using abuses on them factors in a lot more than certain character builds.