There is a reasonably noticable difference between a std 2wd cooler and a RS500 style one when using a std T3. The response and lag is better with the 2wd cooler, so I'd say better to stick with the std cooler as long as you are'nt running more than around 20psi.

Obviously if you are running the T3 very hard, the charge temps can get quite high with the 2wd item so an Rs500 item would be better in that instance, but personally Id rather have the better response of the 2wd cooler and little lower boost. Overall more pleasant to drive.