I always thought (and I used)_that any "good" valve job had 30/45/60 degree cuts on the seat, and 45/30 on the valve, to get the proper seat width. I have done a couple of heads for street engines, that I used 30 degree seats, that seemed (butt dyno) to help low end torque, and economy. Caveat: these were heads that needed a valve job to start with.