For your usage, stay with i7-3xxxQM. XM is almost double the money of the most expensive QM, almost 3x the money of cheapest QM
QM run at 45W (except a few that run at 35W). XM stock runnning at 55W, can run down to 45W and go up to 65W. That's all.

For that kind of money, I rather spend it on getting a larger SSD

For someone who want to pay 3x the money for 15% more CPU performance

Most likely when Haswell get to the market around Sep13, you will probably find the middle range Haswell quad core will match your most expensive Ivy Bridge XM