I thought that ramping was used because a typical cutter does not like cutting to its centre, or at least doesn't cut too well. I use it in ply and similar as it's trivial to do with vCarve, and I aim at maybe a couple of cutter diameters for ramp length with DOC about half cutter dia. Not very scientific but it works for me! Slightly lengthens cut time as vCarve ramps down, and then has to cut an extra ramp length on each pass to bring the whole cut to depth, but that's not really an issue in my non-production situation. I don't (not sure that I can) change any feedrates for ramping without editing gcode; you already have plunge rate which is probably limiting things, and during the cut you are removing less material than during the cut proper. Works for me, but I'm sure that there is a proper answer...