New to the forums here. I just went through pretty much the same situation as you're thinking of doing. I had an '07 loaded E90 335i for 4 years and recently picked up a new '13 e92 M3 DCT ZCP. The only mod I had on my 335i was a Turbo Timer 2. Comparatively speaking, well, you can't really compare the two cars. They are two completely different animals as far as performance and driveability goes. Here's my initial impressions (note: I only have 1,800 miles on my M3 so it's still new to me)
- The 335i is a gentleman's car. Decent looks with decent power. Ride was plush and all around performance wasn't bad. It's one of those cars you look at and go "that's not a bad looking car" yet it looks like every other BMW out there on the road. Yes, I've even tried to unlock someone else's car in a parking lot thinking it was mine.
- The powerband in the 335i I miss for DD (comparing to the M3). The car had good torque at pretty much all speeds and when you mated the gas pedal with the floor it was surprising "spunky". Not fast, but spunky. Nice and smooth acceleration with very little feedback from the exhaust note. It's not the kind of car you would show off the power to your friends. Granted, you had a JB4 on yours so you were a little better off than I was with my TT2.
- As many have said before, the M3 has a raw feeling to it. Its a drivers car. You feel the road and it doesn't give you the sensation of driving on pillows. It's not harsh, but it is a firmer ride even on the comfort setting. Road noise is more prevalent as well. It's not bad but you can tell the nice, soft, squishy "gentleman's" suspension of the 335i isn't there soaking that stuff up. If there is one thing I love most about this car is the suspension. It's mind blowing how much more you're in tune with the road. I had a modded '05 STI before my 335 and the ride quality for DD is remarkably similar between the two cars (e.g. potholes, ruts in the road, stiffness). Handling couldn't be more different with the M3 clearly taking the lead (haven't taken it to the track yet though). Its easily the best driving car I've ever driven. I couldn't be happier to be connected to the road again.
- Power plant wise the M3 is the clear winner in this category. As I said earlier, While I do miss the torque of the 335, the M3 makes up for it with its high winding v8. I quickly forgot about everything I thought my 335 did right in terms of power and haven't looked back since. While I wouldn't call the car a "beast" like many do, it's got plenty of power and you should not be concerned in the least bit about whether there is anything you'll miss about your 335. Granted, I can't speak to your JB4 - those make good power - yet I'll bet you would be happily surprised when you slip behind the wheel of the M. Power comes on fast and strong. It's immediate and pulls all the way to redline. The sound of a V8 is especially nice. I love the DCT as well. Very happy I chose that.
- Looks wise the M3 wins hands down. No comparison.....does not need explaining.