Like many aspects of fly fishing, one answer will not fit everyone or every condition. If fishing for trout most of the time, the largest tippet I use is 5x. I may use 4x if throwing huge wind resistant flies, but most of the time I am throwing 5x, 6x. I and others have landed huge fish on 5x & 6x. When fishing small flies, use small tippet. You may lose a couple of fish here and there, but you will get much more practice of actually hooking up. 4x on a small fly looks like a piece of rope... (Again, my opinion).
Heavier flies equal stronger tippet. That is basic fly fishing. If you get too techincal, then wind, fly size, casting ability, how pressured the fish are all come into play. If I am fishing small cuttys in the middle of nowhere that have never seen a fly, I still use 5x because I am throwing larger more wind resistant dry flies. When fishing for BIG spooky bows on local water that sees a lot of pressure, I may throw 7x and have a plan on landing the fish once hooked.
I personally use Mono on dry flies and flouro on nymphs. Most mono is neutral (if using a dry, it floats, if using a beadhead, it sinks). When using flouro and dry, I have witnessed the a slight belly in the tippet between the floating leader and the floating dry fly, this causes more drag, not a good thing.
You will lose some fish when playing with smaller tippet, but it does up your game. You will notice an increase in take rates for sure. You may not land all of these fish, but you will notice more strikes. I personally am a big fan of 5x. The line companies have made huge leaps in recent years to diameter / strength of tippet. If I had only one spool of tippet to use, I would choose 5x hands down. It works great on furled leaders as well, where you have much longer lengths of tippet compared to that of a tapered leader. Hope this made sense as I kind of got rambling on…
Thanks
