I haven't read the benchmarks... But go for mhz rather than cores. (Amdahl's Law)
Speed: i5 @ 1.3 GHz vs. i7 @ 1.7 GHz
Cache: 3MB on the i5 vs. 4MB on the i7
So yes, the clock speed is higher -- but I'd assume that much of the increased performance comes from reduced cache misses due to the larger cache size... (correct me if I'm wrong).