the one thing that gave me both better detail AND higher speeds was getting a tapered ballnose bit. It does not work for all designs, but it works great for landscapes
https://smile.amazon.com/gp/product/B015C61XX4
with that, the roughing is not super critical, so if some valley isn’t cleared, the tapered bit will just plough through it… so roughing with only the 1/4th bit is fine.
I use 60ipm feedrate with this bit with a smallish (10% or so) stepover… the tapered part makes this thing strong.
(examples at The three volcanoes of N Oregon and S Washington and Red Pin Terrain carve)