Recommendation:
If you have a low budget spend as much as you can on disks, install bare-metal Hyper-V R2 (no license required) split your system into at least 2 seperate RAID arrays (preferably multiple RAID-1 sets over RAID-5's) this will alleviate your IO bottleneck on the host.
Then split your IO loads across the arrays, the bonus is that you can introduce additional storage down the track and move the VHD's to these if you find IO bogging you down. If you need to expand to more iron, then moving a VM is much easier than redeploying from OS upwards. Don't be too concerned about moving back to hardware or other hypervisors, most backup solutions (acronis, ghost etc) will help you do this by stripping the HAL during a restore, or for easy 1 time migrations of (almost) live systems use a product like Doubletake Move.
