since I dont have a code book handy, and I tried an online fill calculater...lets pose this question: 3 #6(Thhn/Thwn) and 1 #8 (thhn/thwn) in one conduit (NMRC) IE PVC, underground, unless I have missed something, using area per conductor, I should be able to use 3/4. I dont feel right using 3/4, I want to use 1"
Whats your thoughts?

This is for a hot tub rated at 50 amps, about a 150'-200' run

I use 1 inch regardless of what I can get by with. Easier pull, less strain on conductors.

MI sparky- since you gave me a left handed compliment I looked up the numbers for you:

Your total wire area in sq. inches is .1887 and the 40% fill limit would allow you to use ¾" Schedule 40 RNMC (.203) but not Schedule 80 (.164). As Tech Home said I'd probably run 1 inch because it's easier especially on that length of run. Wish you well in your career move.