My answer is based on real-world experience with VMWare, running on laptops/desktop drives/15K SAS disks/Consumer SSD's
I haven't really poked around with HyperV too much, but VMWare can rapidly hit high IOPS because of the way it manages RAM and virtual pagefiles. Attending a couple of VMWare seminars sales-pitches, they always cite IOPS as the biggest bottleneck to VM performance.
Perhaps HyperV is less demanding, but I'd imagine it's still going to be very IOPS intensive. OP states that he's only getting usable performance from 2 VM's on a 7200RPM desktop disk, seems similar or worse than VMWare to me....
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