^I really, really, really strongly recomend that you don't do meth. I used to do meth, and it's the most addictive drug I've done (out of many, including heroin, crack, cocaine, amphetamine, benzos, etc.). Every time I did it I stayed on it for a week straight, and as time progressed I started using it more and more regularly. I started off using saying I'd only do it once every 2 months, but eventually I was doing a binge it once every 2-3 weeks. It's also more neurotoxic and physically toxic then amphetamine. I very strongly recomend staying away from meth.
That being said, dosage would be harder to determine due to cuts. According to erowid-
http://www.erowid.org/chemicals/meth/meth_dose.shtml
So if it was totally pure around 10-20 mg would be a good dose. But it wouldn't be totally pure unless you had desoxyn (which isn't pure, but you know how much meth is in each pill, and the meth is pure). Smoked meth feels about like IV meth, and I recomend not doing it if you're going to do meth. When I smoked meth I'd literally just smoke, and then smoke, and smoke, and just smoke continuously all night. I have a friend who ODed, and he kept smoking more meth even whilst ODing. So it'd be hard as hell to study.
For studying I'd say oral or plugged meth would be best. But with meth, a large part of the high tends to be wanting to do more meth. The effects are also different, I have often found meth to make concentration harder and work sloppier because I would always get distracted or try to do 1000 things all at once. The meth crash is also worse then other amphetamines in my opinion. So it wouldn't be ideal for studying in my opinion (and in my experience).
I think the best stims to take for studying would probably be pharmaceutical amphetamines. Vyvance (lasts for a long ass time and can only be used orally, and also doesn't become active till it hits your lower intestines due to the lysine attached to the amphetamine), dexedrine, or adderall are your best bets probably. My preference is for adderall, but a lot of people prefer dexedrine.