Not knowing how you intend to use your car (or even what your car is), it's tough to say what you may or may not need. Even most of the factory discs on GM muscle cars from the 60's and 70's used 1" or 1.25" thick rotors depending on the application, and there's a reason for that, so I wouldn't assume that you would be fine or happy with less if if you can "get by" with it. IMHO, it would be better to err on the side of caution and have surplus braking capacity versus a deficit, but I'm a "brake guy" so I won't pretend not to be biased.

If your brakes are marginally sized for the type of driving you do, the best thing you can do to increase your braking capacity without upgrading to larger rotors is to add cooling ducts to get the most from what you've got. There are a lot of kits in between the smallest Wilwood kits and the 14" Brembos on the new 2010 SS Camaro, assuming that's what you're referring to, so I'm not sure where you were going with your comparison. My $.02 FWIW, get the biggest brakes you can fit in your wheels and budget...you can never have too much brake.

Tobin
KORE3