I've been fishing an Orvis 1 wt rod regularly for the past 15 years and have never felt undergunned for trout up to 16". For the sake of being honest, I have gone mostly reel-less for the past 3 years, but that's another story.
One thing I will say, there is no need to restrict yourself to only the small stuff fly wise. A one weight rod will comfortably fish a size 14, maybe a size 12 or 10 unweighted fly.
If you think you are going to be hooking into some larger fish, be sure to use an appropriate sized leader so that you can aggressively fight the fish.
If you are interested in doing some reading, there are some interesting articles published here -
Ultralight fly fishing for most warmwater, coldwater, plus some saltwater species -- with Bill Byrd