^ I am not sure highly restrictive blocks will give the best long term results.
We used a standard micro channel design, with very good results.
The issue with very restrictive blocks is power. Do you want to add another 50W to your system just the get another 1-2C off your CPU?
Not to mention the costs
Personally I like the current blocks by Swiftech, DD and D-Tek.
Good flow, very good C/W, and low power requirements.
Right now as people have proven on this board, your heat exchanger is the real factor, not the cooling block.
But even so, will likely have lower flow / higher pressure version.
Just be aware, you are slowly getting out of the range of any small pump, and going back to large units again.
Of course a couple of DDc's or MAG's and your in the 8-10 psi range, make real sure you have no leaks
