the XP-90C is made out of copper, not aluminum like the XP-90 is. That means it weighs a lot more and cools better.
For a winchester, the stock cooling is fine. They run very cool. If you really want a different heatsink, get the XP-90, not the XP-90C. The XP-90 will cool very well, but won't put the extra strain on your motherboard that the XP-90C would because of its weight.