22 Disks is what I would often recommend for a SINGLE random write heavy application. And RAID 50 is a poor choice for write intensive application. You've way under spec'ed your storage if you are trying to run 80. You are probably only talking 1000 IOPS with 22 10K disk in a RAID 50. You could double your write performance if you swap to RAID 10, but even then you really probably need 100 spindles to even have a prayer.
Just based off what you mentioned in your OP about 80 write intensive VMs, I'd be recommending 100+ 15K disk and RAID 10 as a starting point. .