I have 1/2 x 10 single start lead screws on my 14"x14" router. I had second thoughts for a while but these are working well for me. I think 1/2 x 8 single start lead screws would work fine for a small router too. (I assume you mean single not eight start in your post)
BTW I can do rapids up to 75"/minute but have set my machine to 30"/minute because that seems fast enough for me right now.
my 2 cents