If you want to be really confused, measure the ramps on "original" barrels. They are not all the same; though one never knows when or how they "got" different angles and widths.
When I cut ramps for GT, I cut to the 50 degrees he likes; when I do them for myself, I go closer to 47. I find they feed better- or at least I've convinced my self that they do
. JMHO.
Extractor cut at spec is not a big issue. I don't use the two key cutters; but a Round over cutter.
I do start the cut with a normal end mill, no use wearing out the cutter removing the first "big" cut.