Both the Powerglide and the TH350 have direct as the final or top gear same as the stock 3-speed.
Years ago I had a '66 that had a Powerglide and it seemed to work pretty well, but it was a 327.
Today I have a '72 with a TH350 and a 350 and it drives pretty nice.
The Powerglide would use a little less power and if I remember right weighs slightly less than the TH350. That might have some performance advantage with the smaller motor, but I doubt it makes enough difference to matter.
