The link to the C&D test from the April '07 issue in question is here:
2007 Infiniti G35 Sport, 2007 BMW 328i - Comparison Tests - Car and Driver
As the article mentions, back in March of '04, C&D picked the G35 over the E46 model 3 series. However, now pitted against the E90 model 3 series, they've shifted back to the BMW.
The article plays out fairly predictably. Although the G35 dominates the acceleration and lane change tests, has more front seat and trunk room and represents a better buy, the BMW wins on refinement and overall driver satisfaction which are often of a more subjective nature. However, the BMW did pull a higher lateral acceleration and weighs less which probably allows it to feel a little more agile.
Honestly, if you were purchasing an automatic (as most do) , I dont' know that you'd experience the gearshift quivering issue mentioned in the article as that was a manual version.
However, ignoring reliability based on the short lease term you mention, I'd still lean toward the Infiniti in build quality. I don't know if MB has cleaned up their act, but MB's in the not too distant past had panel gap issues, were rattletraps, etc. Although the VQ might have lost out in smoothness to the BMW inline 6, I'd wager the VQ would be an order of magnitude better than any V6 from MB. The Nissan VQ engines have historically won several engineering awards from various industry societies for it's build quality, smoothness and reliability.
Dook, only way to know for sure it to get seat time in both cars. Unless you sit and experience it for yourself, things the C&D editors mention might not even catch your attention. I'm sure one will come away a winner in your book. Hopefully, it'll match up with the impressions that your fiancee has as well.