@axodys A major consideration is the MacBook Air goes into conniptions (the processor temperature hits 100º under any sort of load).
Info from MacTracker shows the GeekBench 5 scores of the dual-Thunderbolt 13-inch Pros to be significantly higher than those of the New Air. It's my belief that it's related to that thermal overload problem. As iFixIt mentioned with their tear-down: the fan moves air past the processor, not over it.
The air's processors are not designed for use with a fan, another (I
forget which) source claims.