KF,
My preferance is to use VERY heavy leaders when fishing streamers. I'll usually cut off nymph tippets when switching. For most streamer fishing for trout I like a leader with at least 8lb test and usually use 12 or 13lb test. I find this doesn't effect strikes and you can pull off snags. Also, when you're streamer fishing you will often be casting down and across current and the hits are hard and often come from big fish on a tight line. Considering this, a typical nymph tippet of 4X or 5X will often break. Definitely go heavy with streamers. You can also use a shorter leader. On days when I'm switching back and forth (which is frequently) I'll nymph fish with a 8 or 9' leader with a 2' tippet of 4X to 6X if the water is clear and the flies small. The next section of the leader would be a foot or two of 12lb test. When switching to a streamer I merely cut off the tippet with nymph attached and carefully roll it up and put it away to be re-tied later, then tie my streamer directly to the heavy second section.