I work as a machinist in a small fab shop with machines that probably aren’t half as rigid as yours. I fix/repair bearing fits, make brackets and some general machining. The cheap Chinese cnc lathe we have seems to give me better results with SFM around 150. But that being said I also cheat a little and calculate rpm by multiplying (SFM x 4) / diameter, so that actually puts my rpm a little higher than if I calculated correctly. I am also using indexable carbide from random suppliers nothing fancy. In the mill, it’s all carbide end mills and cobalt drill bits. Stainless is about all we mess with due to working in the food industry, 303, 304, 316, some 400 series. I tell most guys that come into the shop with limited skills to slow down the rpms regularly, they melt drill bits and snap end mills by the bucket load daily. We are not a production shop by any means so the equipment gets mishandled and coolant is something that goes in their radiator, if you feel me. I said all that to say, I get the fact that high speeds/feeds are obtainable but to most home shop guys, slower is better IMHO. Sounds like you have an interesting job, thanks for sharing your experiences. Keep on making chips of some kind.