I know, the G35 is cheaper. The BMW uses more expensive parts and has a higher MSRP, thus, insurance is more expensive.
I would say wait for the 07 Sedan. You will be very happy

The M35 and M45, in its first year, ousted lexus and other models for reliability. That means a rather new design, and entirely new platform, performed better than other tried and tested platforms. Infiniti is using this new platform in the 07 G35. I would not doubt that the new G35 will be even more reliable (if thats possible) than the current one. Currently, we have had zero interior or mechanical issues with our M45. I have had a few interior issues with my 05 G35 (just rattles really) but no mechanical issues. And I believe that the 2007 G35 has a better looking interior than the BMW. Really, I never cared to much for interiors, but I am very attracted to the M series and new G35 interiors. (even tho I think the new G interior looks more like the redesigned FX interior than the new M interior)