Guys, this is a street car, it's not an all out race car, when was the last time you used the trans brake and 2 step at a red light? What are you gonna do when some punk in his Dad's corvette jumps on you while you're doing 35 in high gear? 500 hp isn't that much, a WELL built 650 would surprise a lot of you. I'm not saying it would win any dyno contests, I'm just saying that the carb that achieves the highest peak number isn't always going to be the fastest in all situations, now I know Troy could probably set him up with a pair of 1250's that would knock 2 seconds of his 1/4 time
but 500 hp is 500 hp, the power an engine can make is based on the parts inside of it, a larger carburetor can't make any of those parts do their job any better than they already are, unless of course it really is too small, if you know what you're doing a 650 is not too small for 500 hp. Using Dave Braswell's formula (I'm sure you guys may have heard of him) of 1.3-1.4 cfm per HP you only need a max of 700 cfm to support that, getting 700 out of a 650 would take me all of about 15 minutes, without increasing venturi size, 800 isn't really a problem, more than that is possible but then it would be cheaper to buy the 750.
I will say this, a very common thought about carbs is to run the biggest you can get away with, without very expensive fuel metering circuitry (like Troy's Webber plates) what you are going to end up with is slow moving air at the boosters which will result in slow engine acceleration, my philosophy has always been to run the smallest carb that doesn't hurt the power, higher air speed=faster acceleration. In any type of racing the amount of time you spend at max. power is only a fraction of the time you are running, to take advantage of max. power you have to get there first.