If a wire breaks, or comes loose, or you wire something wrong, the G201 will die instantly, the G202 won't. To me, that would make it worth the extra $20
As for the G212, you really would only need it if your PC can't output steps fast enough to keep up.
With Steven's example of 10 tpi screw, and 1/10 microstepping, you need 20,000 steps/inch (200*10*10). With Mach3's limit of 25,000 steps per second, that's 1.25 inches per second, or 75 ipm. If you want to go faster, and your PC is fast enough, you can increase Mach's kernel speed to 35 or 45 Khz, which would give you 105 ipm and 135 ipm, respectively. If you want to go any faster, you'd want to use the G212.
I'd personally go with a higher lead screw, as that 10 tpi screw will probably start whipping around pretty good at those higher rpm's.