I think it depends on how much light is available and the objective size.
With plenty of light, a smaller 15-45x scope will do anything that a 20-60x scope can do of similar quality because for one, there's plenty of light and two, that extra sun is creating more heat waves and distortion so the higher magnification is worthless.
With that said, as light decreases, the amount of light coming through becomes as important as the glass quality, perhaps even more so at twilight.
So in my eyes, it is a big like a rifle caliber discussion. Can a smaller caliber do the job? Probably. But a larger caliber just has less chance of failure. Lately, that better chance against failure has had me packing a heavier scope and tripod. A heavier load just takes a bit more work. But a loss of invaluable information out there is devastating.