My wife drives the G35X and it is a terrific, trouble free car. I also have a good dealer and a sales guy that works very hard to make the deals work. So when I was looking for a car, I looked at the G35, along with a number of other cars. It is beautifully finished, and solid as a rock. However, I drove the car in the rain, and the performance tires that come with the car are not very forgiving. When the salesman was pulling out of the lot, prior to giving me the wheel, he did a pretty severe fishtale on a heavily traveled road. It really has to be babied in bad weather, even more than the GTO.
That said, I would go for the G35X (AWD) in a minute. I know that the 6 speed coupe is supposed to be quicker than the AWD, but it just didn't feel much quicker (although the car had just come in off the truck and hadn't been prepped). The AWD system in the G35X is very sophisticated, and it is the only AWD sport sedan that I know of that will go to 100% rear wheel drive bias during performance driving. The big drawback the the AWD is that you can only get it in an automatic, and the driver controlled shifting is only mediocre. But it will hold it's own in speed and performance with the 3 series, while giving you the room of the 5 series, with the AWD thrown in as an added bonus.