I have to give my 2c worth here having just sold my 335 sedan to buy a CSL. A stock E46 M3 is not as fast as a 335. I sold my 2001 E46 M3 SMG to buy a 335 2 years ago and was very impressed with the broad range of acceleration that the 335 has, whether it is from zero to 100km/h or from 100 to 200km/h. The 335 lacked that special character that an M3 has.
I always missed the look and feel of the E46 M3 and decided last week to get an one again. I would most likely have bought an SMG , the SMG II was a big improvement on SMG I (my 2001 SMG was the earlier version). As luck would have it I found a very clean and low mileage CSL but was looking primarily for a clean E46 M3. SMG is a personal choice, you should drive it a few times I think to be in a better position to decide. Its difficult to be objective when you really like the car! Drive a manual M3 too so that you can compare them if you have the time. For me, the blip of a downshift in an SMG is the sweetest sound you will ever hear!
From a financial point of view, the main trade off is that the E46 will have a limited amount of time left on its motorplan, it can only be extended for a maximum of 2 years beyond the initial 5 year period.
I decided that speed on its own is not enough, the E46 M3 wins hands down. I am prepared to take the risk when the motorplan expires in June next year.