For the use you describe (i.e. small streams), I'd stick with a 5X tippet at the largest, and have 7X ready if you're planning on fishing any flies 18 or smaller. Personally, I don't bother using separate tippet. I start with 12 ft 5X or 7X leader for trout, and when I trim off the last 3-4 ft from tying on a bunch of flies, I use the leader for bass pond/lake fishing since now it's perfect for that. Then I can use another couple of feet of the leader and then I chuck it. I keep 9 ft 5X and 7X leaders handy for windy conditions or small streams since a 12 ft leader can simply be too long to load the rod well when casting space is limited.
If I only had one leader, I'd recommend going with a 9 ft 6X leader. Use the last 2 ft to tie on flies, and then add 2-3 ft of tippet when it gets down to 7 ft.
My passion for catching fish is eclipsed only by the fish's passion not to be caught.