The 2010 Shelby GT500 is getting mad props for it's ability even compared to the 08/09 GT500.
The car mags were all surprised by how much an improvement the 2010 GT500 was and how great it handles and feels.
I think it did something like .93g on the skidpad.
Steering feel is suppose to rival BMW's now.
The solid rear axle is a drawback IF you plan to track the car for money/prize, or are a canyon carver and want to push the car to 8/10th on the public roads that may have potholes and such.
Other than that, it seems like the solid rear axle hasn't dulled it's handling much. Again, many of the car mags were super surprised by it's ability.
I guess it's now a low 12's @ 115-116 mph car (compared to the previous GT500 which was a mid to high 12's @ 113 mph car.
And as you said, it's simply a cheap pulley and tune away from 120+ traps, and with DR's probably mid 11's ET's.
You'll get crazy amounts of attention in the 2010 GT500 I'm sure.
Pull up to a car meet and people will want to check it out.
All that can also be said of the M3, but you'll see more M3's than the GT500 that's for sure.
If pure gusto and muscle along with very good handling ability for a 3900 lbs car is your thing, you'll surely love the GT500 more than the M3.
However, if you are looking for a more all around car that can work as a luxury cruiser too and show up to a nice restaurant in, or a business meeting, the M3 would be the better choice.
The M3 is fast, and can be modded, but it's mods aren't cheap and you won't get anywhere NEAR the increase in power from the mods on the M3 as you will on the GT500 (unless you s/c the M3 and that'll cost you $18 grand plus!!)
Bang for the buck the GT500 is your better choice again unless you are planning lots of track days, in which the M3 would be better suited.
Drag car? No doubt the GT500
They'd both be awesome to have in the garage that's for sure.
It's a tough choice.
If insurance costs mean anything to you too, check them out.
For me, on my insurance company (Progressive) the M3 cost about $1,200 more to insure each year. Some of that is because the M3 costs $15k more. Some of that is because undoubtedly the M3 costs more to repair if damaged.
Too me, you can't really lose with either.