Top fuel cars are direct drive... Who needs a transmission with 8000hp? That would be silly, and would break alot.
MANY, Many purpose built drag cars still use a 2 speed powerglide... How's that for archaic technology! The fact is, torque converts are excellent in very high torque applications. There is far more control over rear end of the car since it's magnitudes easier to keep traction right on the limit of the car's acceleration. Imagine trying to launch a 600Hp musclecar with slicks using a regular clutch :rolleyes:. You'd never get it right, and by the time you do, it's time to shift anyway. You can use less gears with an auto since the converter effectively multiplies torque (makes no sense, but that's what I read all the time). Not to mention that auto's by their very nature can handle more torque throughput than a regular manual can, simply because of planetary gear design strength.
I don't think I've seen many if any 9 second / 10 second cars with 5/6 speed manuals. More like 2 or max 3 speed autos.
Being in overdrive has nothing to do with anything I'm afraid. Your transmission just broke Top gear on any normal transmission is an overdrive gear (less that 1:1)