With your car running what it runs, if it has the 1.76, you may get away with it. If its the 1.82, it won't live long. My biggest concern with any stock planetary set including the 1.76 is the unknown history behind the planetary. How much abuse did it see before putting it in a race car? How long was it in a race car at what power and weight? Etc.
As far as cars going faster with glides over 3 speeds, that all depends on the combo. My car weighs 2825-2835 depending how much fuel Im carrying. Friend of mine has a car that weighs 2840 that he just put a faster engine in. I have a 727 and he has a glide. At my 5.38 best I ran, my 60' was 1.17, 3.43 at the 330 and 5.38 at 125.74 mph. I have gone 127 but not on that pass. My friend got back on the race track at the Halloween Classic at Norwalk after having open heart surgery back in August. His car ran a 5.35 at 129.28 mph. His 60' was 1.20, 330' was 3.45, and 1/8 was 5.35. Granite I am not there to see what my car would run this weekend, and he definitely has more smoke than I do as he is 572 B1 Move center head with tunnel ram intake. But for comparison sake, best ET to best ET, this is a PRIME EXAMPLE of where the powerglide comes into play. He has faster ET, but his increments aren't as fast as mine. Him and I have been running within a tenth of each other since I built my Demon. At times, I was faster then him, but his MPH was ALWAYS higher than mine. This is the powerglide taking less HP to rotate and less parasitic drag.