T51 like most hks stuff is very expensive for what you get, good option going gt40 should last for ever at those sort of boost levels.

The ebay coolers should be ok, the 200sx ones are fine lots of cars in the 500bhp region use them. Then again I remember Gary from apt saying the ones for the evo's were worse then the oem cooler. Whats the opinion of them on the rx7 forums?