Unless you're using the worlds worst CAM, rapids will amount to a VERY small percentage of your total machining time - typically just a few percent. As Hood indicated, higher acceleration is of more value for most applications, especially for 3D work, where low acceleration can increase your machining time many fold. 100 IPM is a perfectly reasonable rapid speed for a BP, and you'll gain little by going much beyond that. As Terry indicated, you start going too fast, and the machine will start shaking, and walking all over the shop. Plus, of course, when things go wrong with fast rapids, they can go very wrong, VERY quickly - before you have time to hit the big, red button. I have servos on mine, and it's quite capable of running 350 IPM, but I run at 200 IPM, because there's just nothing to gain by going faster, and the chances of a destructive accident are much greater.
Regards,
Ray L.