A properly ported or a BBK throttle body is worth 10 or 11 horsepower. There was some discussion around removing the Intake divider, going with a single blade throttle body, extrude honing the Intake, etc on this and other forums.
I went through a few Intake variations on my own with the standard see-saw between HP and Torque: One goes up and the other down.
The Gen III Intake manifold obviously works, but isn't great in the big picture.
Here are the differences you asked for, in a nutshell...
Trainman and I went 2 very different routes.
He went with a race-style engine: 561 cu. inch (via Stroker crank), ported Gen IV heads, mechanical cam 248/256 .720" on a 112 C/L, high compression, Intake (Gen V, I think) manifold, open exhaust, race fuel, drag suspension setup with skinnies, lightweight doors, windows, seats, lowered front, aero improvements, i.o.w. all the important stuff you would want for racing.
4500 pounds w Driver.
I went with a pump gas performance street engine: Standard 505 displacement, unported Strikers, mild hydraulic roller, 11:1 c.r., ported throttle body, Gen III Intake manifold, 4 cats with full exhaust, stock gearing, stock 2-piece driveshaft, stock front tires, stock suspension/stock ride height, etc; 2800 stall convertor.
5600 pounds w Driver.
Both engines produced 1.5 horsepower per cubic inch when you do the math.
We are ho'ing Kiwi's thread and may be punished!!!