If anything that is requiring all 4 cores on the i5/i7 for a prolonged period of time means performance drops to the i3 level anyway, why would I buy an i5?
You bring up an interesting question. The CPU benchmarks show the i5 is faster, but what task can an i5 MBA do that an i3 MBA cannot?
I think an i5 can generally do the same tasks faster. However, PC Mark 10, a home productivity benchmark, suggests an i5 MBA performs similarly overall to last year's dual core MBA.