Powerglides are fantastic racing transmissions!! I've used them and I swear by them for light weight drag cars, (2,800 lbs. and lighter). Above 2,800 pounds, you start to reach the entry level to the laws of diminishing returns. For a really light street car, a "glide" can still be workable, BUT!! Newer technology and advances in transmission parts and electronics have made incredible advancements toward durability and drivability!!
The new OD transmissions provide a 20% or better effective ratio which increases both fuel mileage and engine life. Add to that a good lockup torque converter and, depending on overall gear ratio, you can reduce engine RPM another 250 to 500 revs. That's a LOT considering that if you're traveling 60 MPH, your engine turns over 250 to 500 fewer times per mile!! In a hundred mile trip that's 25,000 to 50,000 revolutions!! At 2,300 RPM and running 60 MPH the lockup converter reduces that to under 2,000 RPM, splitting the difference of 250 and 500 to an average of 375 RPM! Around a 14% reduction!
My last drag car would turn the quarter mile in less than eight seconds and peak RPM was 7,200. That works out to less than 1,000 revolutions across a quarter mile distance and it should be pointed out that that's figuring running wide open for the entire distance! Yeah, I know that I'm not counting driving from the water box to the staging beams or revs turned in the "burnout" procedure, but for a simple discussion, we can leave those figures out.
25,000 more turns of the crank under ideal conditions would mean a lot of extra passes on that race car!! That also amounts to many more miles on your street car!!
A LOT of laps around the Dairy Queen!!!