I have a 14", 1 1/2 hp Craftsman. I rarely trade out my 3/4" blades for anything smaller, but when I do, 1/2" is as small as I've needed to go.
More important than blade size or tpi, imo, is having your saw set up well, and especially the guides and backup bearings properly adjusted. I got the Carter bearing guides for my saw and it made an appreciable difference. Don't try to use a blade too long, when it gets dull, get it out of there.
Love my bandsaw. It was the first big power tool I bought, and would be the last one I'd ever get rid of.