I tried that in the beginning with just two 45CFM fans (Yate and the Scythe IIRC)....works well. I haven't tried with two counter-rotating fans (the Delta Triblade and the AC12 both spin in the wrong direction). I'll try the Delta Triblade LE and another similar fan....see what I can pull.

Also, the AC12 seems to be completely incompatible with my testbed. Either that or it sucks. Open framed Thermaltake worked okay and the reverse-spin Deltas were okay....but the AC12 just blows.

Just tried the Delta LE Triblade (72CFM) on top of a Sharkoon 2000....both at 12V. 103.7CFM, 40.7dBA, and 85.3CFM on the radiator (only a 17.8% drop!).

For comparison....the San Ace does 100.5CFM at 40.7dBA and only 71.8CFM on the radiator at that voltage (10V).

When the Sharkoon is placed on top of the Delta....both at 12V: 108.6CFM, 40.9dBA (higher pitched though), and 90.5CFM on the radiator (16.7% drop!)