[mopar5150]

Interesting and a good idea making a completely new heatsink. I would like to see any photos you might have.
With the fan I use under the V-pro I have not had any temp issues even with quad 800s and 8gig ram. I used to add a small duct like the factory setup but found it was no help and perhaps a hinderance. The extra air sneaking out of the small holes of the V-pro back plate appears to make a difference. Adding the slot to the side of the large exhaust fan is required as well.

I have made a lot of these "clone" systems with no temp complaints. I think most people realize that these wont survive in an 90f environment for very long. My desk where I use this same setup maintains 78f and I have not had any issues.