Well, ATi cards use AMD's Catalyst Control Centre for managing them, which includes basic overclocking.
Using ATi Overdrive, in CCC, you can just slide one bar up for the memory, and another for the GPU itself (it looks something like http://i.imgur.com/TL2KW.png , though I'm not quite sure how it'd look with two cards?) It is somewhat limiting however, and there are third-party tools that allow you to push them further.
Given that you're looking at the VaporX model, which is itself a very good cooler, you shouldn't really get another cooling solution.







