They perform better with stronger fans, yes. But the stronger fans cost about ten bucks each. Sanyo Denki San Ace, Panaflo's, Sunons, pretty much any 120x38mm fan will do. Petra's have them I believe.
But the most important thing with heatercores is to use a shroud. I used to cool my 1900xtx and opty 165 with a single 120mm fan and a pair of heatercores. Talk about quiet!