It's hard to say. None of these chips will likely have significantly lowered lifespans unless you really crank the vcore. The E6600 could be thought of as having a shorter lifespan due to the fact that lots of E6600 chips out there seem to need more volts for good ~3.6ghz overclocks than the E6700 needs. The multiplier just doesn't seem to be the issue, it's probably more related to binning than anything else.