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#11
Ahh, caught out skimming - didn't notice that pertinent part
In that case, splitting the partition is definitely the best way to go given your requirements.
Like pretty much everything else, VM's do benefit from SSD's. There is a noticeable difference when running a VM on a single spinner. Biggest noticeable impact is on load times basically. Starting/restoring is a lot quicker on SSD or RAID than a single spinner. Actual OS operation is fine though.
A good compromise could to be to set up a spinner RAID 0 to run your VM'S off and to also purchase and an external hdd to save all your backups to. USB 3.0 preferably if you have it. If not, there are add in USB 3.0 cards.
RAID 5 would also give you a speed benefit but requires extra hdd's - ie you'd need 4 drives for a 'two drive' RAID.