I use the 225 grain on my 3wt trout spey rod, which is basically a 5 and 1/2 weight single hander. I think either a 5 or 6wt single hander would be fine with that grain weight. You could probably go down some grains tho, 175 or 200 might be the sweet spot. I would recommend using a 5 foot or 7 1/2 foot sink tip for the single hand rod setup.
Thanks for the post, I started with a couple of two handers in 6 to 8wt, but the opportunity to use a light head on my single hander is to much to pass up.