For studying, I find that excess stimulants tend to be counterproductive, I always end up finding something way more interesting to read up about on wikipedia, and the stims give me a sense of accomplishing shit while procrastinating. Study aid and exam aid are not synonyms
I've found a mixture of two racetam nootropics to be invaluable for increasing my memory while studying, those two being Noopept and Aniracetam. A bit of caffeine goes a long way for giving the combination a pseudo-stimulant kick to it.
Come test time, stimulants will help increase your writing output, and articulation but will only be helpful in small doses. High doses will suppress latent inhibition, make you waffle and make writing coherent sentences on familiar topics difficult. You want to feel awake, but not wired. Even for someone with a tolerance from daily use, I find anything over 25mg d-Amphetamine is too much for a test
An amphetamine naive person should not take more take no more than 15mg d-Amphetamine for a test. If you took a daily regimen of nootropics to study, take them on test day, they don't really enhance exam performance per se, just studying which in turn helps exams
Oh and remember, that drugs won't magically read the textsbooks for you
On another topic, @ebola, yeah I'm aware about the memory consolidation issues with Amphetamine such as how you mentioned with time constriction, but does that apply to semantic memory which is what's key with exams or is it simply contextual episodic memory. The former seems unscathed or even enhanced (due to better executive functioning allowing better learning behaviour) by my amphetamine use (although nootropics may play a role here) although I admit there is probably some issues with episodic memory.