Jumping from the bottom to the top of class is not unrealistic. There have been many success stories doing just that. My suggestion here though if you’re going the Demons of Magick method is to go with Vapula first, as his description in the book is more in line with what you’re looking for (ie. an improvement in your learning ability). With belial, im more under the impression that he can help boost your work ethic, but he wont necessarily make you smarter (ie., making it easier for you to understand and absorb the material you’re reading). I’d probably do a separate ritual with him. Crocell as @56cpdb pointed out may be even better than Vapula for what you’re looking for, because he is especially good at helping folks in formal study (ie. college courses). If you do a thorough look through all the descriptions in the DoM book, you’ll see all this