Hi, this is an interest area of mine, although I am interested in all drugs.
Similar dose, similar ROA, similar purity = similar effect, on average. Of course individual responses may vary.
There is research that suggests this (the most important of this research is on human subjects), I know various educated, sensible people that have on occasion tried both and say they are basically the same thing in regarding to effects, when accounting for dose and ROA.
I disagree with the idea prescription amphetamines are significantly different in humans when accounting for factors such as ROA, dose (and accurate measurement of dose), purity etc. At least I don't think this matter is settled.