Right now I can run about 60 IPM without stalling the steppers and I'm pretty happy with that, but I expect I'll want faster in the future. I'm running 12V and anticipate cranking that up to 30-40v once I know how to do that without toasting my motors.
If your not afraid to spend a bit of money, Probotix has a 40v, 10 amp DC linear power supply for $86.
What are you using for your hold down? I'm currently using MDF, but I have delusions of one day building an 80/20 T-slot spoil board. I could make one for about $40, however they want $39 per stick to ship to Alaska, and I would need two 3"x36 sticks. You can get shipping on that down a lot if you live in the states.
-dan