Well this is a csl forum, so you'll no doubt get unbiased opinions
The V8 will be thirsty on fuel ... very thirsty. In fact I often wonder how on earth BMW can ever claim that the new V8 was more economical than the inline 6
(I average 14.1l/100km vs the 11.8l/100km in the CSL - and I don't even track the V8!!) - really should qualify this with the fact that I do a lot of city driving - on the motorway it'll do less than 10l/100km)
The new M3 is one of those cars that the more you use it the more you'll like it. To me it really wasn't a fall in love with it straight away sort of a car, but it is one of those cars that is VERY EASY to live with on a day to day basis. So much so that I find myself missing some of the creature comforts when I step back into the CSL (bluetooth, awesome stereo - don't get the upgrade, the stock 10 speaker system actually sounds better than the 12 speaker system, sat nav ect ect)
It has plenty of if not way more grunt than the CSL and you really don't notice the weight in the car.
The engine really is the master piece helped by the compliant ride.
I'd say if you are not a hard out tracker, then the E9X M3 is the way to go - the value of these have some what stablised now and it'll be the last Naturally Aspirated "M" engine to be produced (next M3 is coming out with a twin turbo inline six) - and the lack of choice on the market at the moment means that people are starting to realise 'value' in the E9X M3.
Another thing to consider is age - the new E9X M3s (except for the DCT) have proven to be a rather reliable car without any major concerning issues, unlike the E46 chassis.