The i7 will be better at multiple threads, and maybe even a tad faster at dual and single threaded processes, but you'll be trading battery life for the extra performance.
It really depends on what you want to do with the laptop; if you just want a desktop replacement, go with the i7; if you want a capable system with a bit more battery life, go with the core 2.
You sure about the performance? The QM is only 1.6 Ghz clock, I would think for single/dual threads the Core2Duo would be better eeven given the improvements of i7. You have any benches for those numbers, I've been trying to find an actual comparison of laptop chips but I can't seem to find the QM pitted against anything.