The plastic stockers heat soak very quickly and are all but useless after one hard pull. IMO that's the primary reason to swap them out, the HP improvements are secondary. The ebay IC's might be lacking in core size, but they are bigger than stock (and presumably more effective) and surely the aluminum end tanks offer a significant improvement over the plastic stocker tanks. Considering the price it seems like a nice setup for Stage III-ish power.
________________________________________ NA to TT, starting from the ground up...