If you're running a full Separatist team and not the IG88 nuke squad, I believe ideally you want him to be a certain percentage slower than your B1. Otherwise, Grievous's turns will come up often enough that his friendly damage outpaces B1's stack regeneration. I don't know what the exact numbers are though.
As for his arrow, a health arrow with a decent (10+) speed secondary would be ideal.