Depends how you want to beat it. In handling, straight line, all around, etc.
In a straight line is fairly simple, you just have to get better traction and make more HP per lb than the '12 does. Seeing as how the 2011 GT
makes about 375hp at the wheels and is about 3900lbs with driver, you should be able to do the math from there. Your cobra is about 3350lbs without you. With just a few select modifications, I've got mine down to 3530lbs with me in it and with the spare tire, and I'm 265lbs!
Ultimately you would need to have at least a weight:hp ratio of 10.4lbs per hp just to equal the new 5.0. In my case, I would need to make about 340whp or about 400hp at the crank to keep up. That's about right, considering right now I'm running about 1.2 seconds and about 9mph behind a similar '11 GT I ran across, but he was also running slicks. I'm only about 0.6 seconds behind a stock '11 that ran last year with my 98.
What I'd recommend is, for straight line:
Upper and lower control arms
31 spline carrier and axles
Ram or similar clutch
your choice of a good shifter (the stock shifter is awful beyond words)
Slicks (cheater or full)
75-100-125hp shot nitrous
will by far be the cheapest way.
Any way you slice it, you're going to spend a solid $5000 or more for a solid setup that won't break on you
My current combination is less than ideal, but it's doing alright so far. Mind you my track is at almost 6000' altitude, so the MPH and ET are slow, but I've run a best of 14.8@95mph, the stock '11s are running around a 14.2@103 when I first saw them last year (probably quicker with practice...103 should be mid-13s).
I've got a fresh engine with mild port matching, port matched intake, 3.73 gears, Pro5.0 shifter, C&L Intake, SCT Tune, Livewires, Fidanza aluminum flywheel (probably hurts more than it helps) no mufflers, lightweight battery, Mickey Thompson ET Street 26x11.50-16s and not much else. I figure at sea level it should be good for a 13.30 or better at 103-104mph.