It's a boring rainy Sunday, so I figured I would throw my two cents in. I've been hanging out on G35 forum for a few years occasionally see links posted to clubrsx.
I've owned owned both the current gen G35 ('07 G35 Sedan) and the current version E90 335i ('08 335i Sedan w/sport package).
For starters, the new G35 Sedans are nice cars (I really don't like the looks of the new G37 coupe). If you were to judge the G35 and 335i just by reading articles in Car and Driver, etc. you might think that both cars are very similar in terms of performance.
Well they're not. The G35 has a high reving N/A engine. You pull off from a stop in normal driving and the tach spins up to 5K and the car is barely moving. The G35 really does not start to pull until 6K. Edmunds review says the 2007 G35 Sedan does 0-60 in 5.6 seconds and that sounds about right.
The 335i on the other hand will do 0-60 in about 4.8 seconds stock but it feels so much faster because the 335i's engine has so much torque at the low RPM it's just brutal. The G35 handles "good" but the 335i Sedan handles like a 4 door corvette.
That said, the G35 does have a more space age interior, and electronic gizmos, and the Bose SOW in the G35 is quite good. The interior on the 335i is much more plain and the 335i Logic 7 audio system, while tolerable, but nothing to get excited about. Overall, the quality of the interior in the 335i is better, better leather, better carpets, just all around better fit and finish.
But the real difference with the 335i comes into play when you want to say increase the stock HP and Torque by around 1/3. With the G35, you would be looking at spending mega $$$ for an after market turbo system. The 335i? Buy a $500 SSTT turbo tuner "black box" and a $300 aftermarket intake that can be installed (and put back stock in 20 minutes) and easily pick up 60hp/60torque. I mean, the SSTT is a no brainer. There must be 1000 people running them over on E90 post and not a single report of a problem or so much as a check engine light.
I drove a '07 G35 for a year, and like I said, it's a nice car, but it's just not in the same league as the 335i E90/E92. I'm not real big on the styling on the 135 (looks like it got hot and sagged in the middle to me) but I know the engine that's going to be in it, and the 135 is going to eat a G37 without so much as a burp
My 335i Sedan: