The M42 is 220 lbs, M44 is 225 lbs. The M50 series (1995 and earlier) weight approx 299 lbs, and the M52 weigh approx 308 lbs.
HOWEVER! that does not include the weight of other items such as exhaust manifold (approx twice as heavy in the M5x series; btw Jess, I wrapped my 2nd header finally. Will take pics soon). This number also doesn't include necessary changes such as front springs/shocks to handle the excess weight, wiring harness (slightly heavier), the few lbs of adding the rear battery connection system, the rear battery hold down that's necessary to keep the battery in the back, the weight of bigger brakes in the front to balance bias, or other little things. Simply, I expect the changes to add more than 80 lbs, perhaps 120 lbs in total weight changes. A CF hood reduces weight by approx 60 lbs. Battery relocation can a good amount of mass, and simple weight reductions such as eating healther are obvious to balancing the weight
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Having driven both swapped ti's and my DASCed ti (which has a little more power than a stock M3 at the moment), I would say they drive similarly when the weight is moved around. The extra 100 lbs is hardly noticeable. However, my ti already has the larger brakes, suspension changes, and a few other weight adding factors that make it close to what an M5x series motor would add.
The best value is to swap a motor in if you know how to do it. Otherwise, a bolt on mod such as a DASC could be a better value as it doesn't require extreme mechanical skills or electrical wiring know-how that a motor swap could.