If you had about $50K to piss away....

[Perfectlap]

take a gander at this month's Excellence.
They take a CaymanS, 997 Turbo, and 997S through their real world paces.
All of these cars were well modified from different tuners. The CaymanS had like $30K in upgrades, the donor car was about $35K and in the driver's opinion was the best per pound and pony. "No matter who was driving the CaymanS, it was right there with the other two".

If power appeals to you, (being that your considering an M3) and you are looking to plunk down $50K, I'd take a look at taking a nice Carrera or Cayman getting some of those tuners who are hurting from the economy to make some upgrades.
Maybe call the tuners featured in the Excellence article directly and see if the have cars for sale.