For the past 3 years I've done about 80% of my trout fishing with some kind of a double-hander. I started down the same path as you're talking about. I got one of the smallest rods I could (I settled on one of Meiser
's 4 wt switches). Since that time I've figured out a few things.
1. A switch rod is no substitute for packing a short single hander for dead drift dry flies. It can be done but, its not the right tool for the job.
2. On most trout streams I fish on you'll catch more fish if you can hit the other bank. Trout tend to hold the banks even tighter than steelhead. Other than big wide tail outs you'll catch 90% of your fish with in 10 feet of either bank. If you can't hit the other bank you're missing about half of your fish.
3. There is no need to throw super light tippet swinging soft hackles, stripping streamers, or skating bombers so, a softer rod is not needed to protect tippet.
4. Fighting fish even with my little meiser
is in no way comparable fighting fish on a single hand 3 or 4 wt. Its all about the take after that it tends to be anti-climactic.
5. Its a real PITA to find a variety of lines for anything less than a 5 wt. You can take you pick from a scandi or a skagit. I know you can fish a long single hand line but, those lines are so light per foot that they can be very hard to get proper anchor placement if there is any kind of breeze at all.
The morel I took away from these observations is that one of the new 12'-ish 5 wts. is the perfect trout rod. I ended up settling on the 5 wt. decho.
I have 3 or 4 lines that work well on that rod but, about 75% of the time I have an airflo
tactical steel head line on there. Its short enough to stay out of the bushes but long enough to throw T&G type casts well. Plus, you can throw light tips on there (t-7 or t-8).
The rest of the time the rivers are either very cold and I want to put the fly right on the bottom or the water is big and muddy and big streamers are the ticket. In this case I throw a skagit with 4 - 10 ft chunks of t-10 to 12. Shorter tips allow you to throw more grains per foot which turns over big streamers much better.
Keep us posted on what you decide. I'm really curious what other people come up with for trout rigs and tactics.
Just my 2 cents, your mileage may vary.