Heh... Until the mid '90s I was a "ford guy". In 1997, I started shopping for my first new car and the first place I looked was the ford dealer. I always wanted a mustang because my Dad drove them at work and the mustangs always seemed to win the bang/buck competitions the magazines held. Then I looked closer at the numbers and saw that the 5.0 mustangs just couldn't keep up with the LT1, the new 4.6 stangs were even worse, and even the 5.0 and 4.6 DOHC cobras couldn't keep up with the 1995-1997 camaros. When the LS1 made it's debut in the F-body and I read 2 articles that showed the LS1 camaro beating the 1998 cobra in every single performance category for $10k less, I put my money down on a 1998 trans-am (I couldn't stand the camaro fishmouth). It had nothing to do with GM vs. Ford, it had to do with performance comparisions, period. I'd driven both the camaro and mustang and I knew firsthand that the camaro was faster and handled better on the track. Since I was putting my money on performance and not on looks, the choice was easy.
On the one hand, I had a beautiful green cobra on the lot marked at $33k that the dealer promised I could have for $32k if I took dealer financing, or for $26k I could have a loaded trans-am that could take that cobra in any competition. Only an idiot would say I chose the TA because I'm a "GM guy"... It was simply a better car for less money, period. It wasn't until 2003 that a stock mustang could beat my car in a straight line and that was probably because my diff is shot from racing and the motor had 85k miles on it, and there still isn't a stock '04 or earlier mustang that can keep up with a camaro or TA on the autox circuit. I haven't seen any '05 stangs running autox, but I'm sure we'll start to see them as the LS1 camaros and firebirds start getting old.
But "ford vs. GM"... That's nonsense. Ford fanatics pull out the mullet and "GM guy" labels every time they're faced with the fact that they paid more money for a slower car. Now that Ford is finally putting out a car that is fast AND looks good, it'll eventually be the GM fanboi league that points the finger. But until recently, the F-body and vette couldn't be even remotely threatened (in stock or near-stock form) by the mustang.
Aftermarket mods... You get what you pay for and any car will go fast if you throw enough money at it, regardless of whether it's ford, GM, or porsche. It's just a bit easier at the beginning with some cars, but everything on the market today has cheap bolt-ons so even that's a level playing field dominated by whoever has the most cash to put into the project.