I would say on average between 2 - 5° C. better depending on the workload. My BOINC workload is very variable and works the cpu either harder or easier but on a synthetic workload like Prime95 or y-cruncher it is very consistent.I know your post is a little old but I've been struggling to keep decent temps with my EK Velocity (I also have a Heatkiller IV). How are thermals on the Foundation vs your Silver + Nickel Cuplex Kryos? Those are the top 2 on my list right now.
I had the Silver + PVD Cuplex Kryos block on it before. And before that I had the XSPC Raystorm Pro. I'm convinced the Silver coldplate of the AQ block and the direction of array flow across the dies is what allowed it to consistently beat the Raystorm Pro by 2° C. I think that the speed of heat conduction advantage that silver has over copper is a good portion of the improvement.