Steve,
I keep it very simple. 95% of the time I use RIO 5X flouro. If I’m fishing extremely low clear water I may drop to 6 or 7X, but my experience is that as long as I get a good drift I don’t need super small tippet. If I’m on a stream with “less intelligent” fish, I don’t even think I need flouro. I usually don’t adjust for fly size. I just try not to use anything below 5X unless I feel its necessary. If I’m fishing high or stained water I won’t hesitate to use 3 or 4X. I prefer flouro, but you will still catch plenty of fish with mono if you get a good drift.
To sum it up for me: 5X almost all the time, 6 or 7 in low super clear water, 3 or 4 in high dirty water.