I own a 02 GTS FE, and a 03 996TT X50. They are completely different cars, but they are both great cars. The 996 is my 3rd, and the Viper is my 2nd. I tried to live with just one, but have ended up with both in the garage. The 996, gives a more controlled, tighter feel, the quality level is very high. It is easily modified, ECU, muffler = much higher (usable) power. The Viper offers brute force that isn't matched by anyone. The power is also easily modified. It also draws more attenion then any car I've owned. I wasn't able to decide on one car, You can't go wrong with either, or both.
Tom
PS- sil350 -I just bought a New 02 GTS FE for 68,000, price of a new 996TT X50 is 136,000-150,000.