I agree with elmo that a 5-series BMW will likely get you more car. Infiniti made this change (essentially a newly tuned 306hp engine) to compete directly with the new Lexus IS350...so you may want to look at that option. That said, the German competitors would be the BMW 330i, Mercedes-Benz C350, and the Audi A4 3.2L. Though I appreciate the Japanese design and engineering, I find them to be more brawn then finesse, plus you'll find newer performance technology generally in the german manufacturers...both these points are ultimately why I have been a german car enthusiast for life.
There are so many differences between all these models (not to mention price) all aimed at a certain type of driver and lifestyle. However, from a strictly performance perspective, the 2007 G35 truly is impressive compared to previous years. For the value (again as elmo said), you can't go wrong.