Question: how many iops do i need?
Answer: Dismal. 50-100 IOPS per VM can be a good target for VMs which will be usable, not lagging. This will keep your users happy enough, instead of pulling their hair. So a Google VM with 40 GB disk and 30 IOPS/GB will be able to peak at (maybe not sustain, though) 1,200 IOPS.