im 24 and earning less than you are, but im definitely set on a zed - a 100 mile commute each week sounds pretty reasonable to me, thats only 4800 miles a year all in, whuch is well below average. if you want a sports car and can afford the insurance, id say go for it! I think considering the fact its a 3.5 litre V6, its one of the best value to buy - your only other options for that kind of pace are either an old school Jap turbo car (Supra, Skyline, RX7 etc) but these will be expensive on a regular basis, or a porsche or Beemer - both of which will have ruinously expensive parts and servicing. Yes a clutch on a zed is a lot, but it would be lot more for an M3!
Whats your car history? driven anything with 280bhp before? As you say, stepping up from a C2 will be a big change... ever driven RWD before? if you havent, get some training, completely different animal!