Expect low 70s with the 500 single. I have been researching the same thing for months. One thing I would stay away from is the twin big block 29, very ass heavy and very very tight engine room. At least the 32's have a little room in front of the engines to do a little maintenance.

32s with 502 mags do about 75, 500's get low 80's on average.

29 with 500 low 70's, 525 high 70's very low 80's, 575 mid 80's

I would highly recommend the 29 with a big single, fuel weight, maintance is all an advantage. I have a 29 Fever with a 540 700 hp. 90 mph boat. I run with a friend of mine with a 32 and i leave him in my wake. I can out power him all the way around.