The stock location is ultimately ideal. The catalytic converter has to be heated up to a high temperature in order to operate properly. Right after the exhaust manifold is the best location for this. The only way I can see you relocating the catalytic converter is actually converting everything from the exhaust manifold to the flex pipe over to an SVT set up. The SVT header is a long tube design and has the catalytic converter under the motor instead of in front of it. Finding a decent SVT cat might be a problem but you can always go with a high flow cat from www.c-f-m.com
. But that's only if you go with the SVT long tube header. Or you can scavenge around for aftermarket headers if you so choose. You may find them cheaper, but the SVT set up is by far the best you can put on your car.