I've done a similar setup at my house for probably similar reasons - solves the problem of friends bringing over their nappy computers with ancient video cards and me having to upgrade that and get it all running every lan party.
I used opensolaris (and now openindiana) for the back end server. It has lots of ram and some SSDs for the l2arc cache so most things end up being cached. I use zfs snapshots for the clone systems.
This works well, and performance falls somewhere between an SSD and a Hard drive for gaming load times... with one exception.. boot times for the diskless systems is horrible. Like 2 minutes each.
It looks like you are booting your windows off VHD and putting the differential on the local SSD? Any benefits of doing that over just running everything from the backend server?
I'm thinking about getting an SSD for mine and using that for the boot partition of the systems, and then having steam on an iscsi mount off the backend server. That should give great performance, and fast boot times. But I wouldn't be able to rollback the OS to the master state like I can do now.
Yeah, so what did you do software wise?