Nice job. Only minor critique is that you've got the GPUs pretty close together. Why not space them farther apart to allow more airflow? You can also angle them differently to catch air from something like a box fan, if you're dedicating a room in your house for tech that is.
The spacing is the standard slot spacing on a motherboard. So it's card, blank slot, card, ect.
All the cards run between 59C and 74C. The 6970's (four of those on the top row) run hotter (in the mid to upper 60's) My 5870's (everything else) all run between 59C and 64C. So they seem to be getting good air flow.
Even when the outside temp's get into the 90F+ range the cards still stay decently cool.
I would space them further, but between leaving space for additional cards, and the limits of the riser lengths, that was the best I could come up with.
The motherboard plates all have the motherboard mounted all the way to the right (facing the PSU and motherboard connectors) which makes the riser cable in slot one a bit short to reach. I modified one of the plates to mount the motherboard further left, and it's a big improvement.
I'm talking to sheet metal shops about getting custom mounting plates made. Two of the design features being added are a standardized PSU mounting area and bracket, and moving the motherboard as close to the PSU as possible. For the power supply mount I'm going to have rails to keep the PSU from walking left/right, a more robust mounting bracket on the PSU face, and an adjustable Velcro strap to hold down the aft end of the supply.
