The one from Wizard are cheaper - https://www.facebook.com/WizardExhausts/
you can also send a private message to Pud237 to learn more about them (prices, shipping, new seals, etc..)
Gain from catless manifolds is about 10hp, with remap and a healthy engine, users usually get to around 270 hp. Getting rid of center cats does not result in much gain, also removing them will result in unpleasent exhaust smell.
If you checked ATC carbon intake plenum, they claim gains of almost 20hp with it and bigger throttle body, so theoretically you can get to 290hp, but I would say this is overly optimistic. For additional gains you will have to take the engine apart and do some more upgrades, but this kind of work requiers a very good specialist.
But before you do any engine tuning, upgrade to limited slip diff (Q2 or Quaife), original ones tend not to last long, and when they get "destroyed", gearbox gets damaged too. Even if you want to put the original 240 hp down to the road, you need limited slip diff, becuase that much hp is just to much for FWD car to handle properly. Doing this is hands down the best mod you can do to your GT.
And keep in mind that the OEM suspension is not up to the task, not to mention when you increase horsepower. So thicker ARBs (eibach) and better shock/spring (KW, Bilstein, Eibach...) combo is required as well.
Always take care of suspension, brakes and traction before engine tuning, always. Check out that page for starters - http://shop.alfisti.net/Tuning-Styli...GT:::1_17.html
If I take out the cats, what hp gain are we talking about? Standard the V6 delivers about 240hp, can I expect another 60hp from a catless system?
I can't even....
This is probably my last post here, you are just to much