I think you are going to get a few different answers here. But my experience is as follows...
For .090 alum (whatever alloy Harbor sales sells) with a spiral single 0 flute, upcut is:
1/4" bit = 12,000 RPM's @ 1 IPS and the Z @ .40 IPS
1/8" bit = 16,000 RPM's @ .40 IPS and the Z @ .40 IPS
Ramp-in the toolpath.
I get the best edges cutting up to .040 and .063 as a single pass strategy.
Two passes for .080. .090.
I have vac hold down. And still use clamps, screws, whatever it takes to make sure that the sheet doesnt move even the slightest little bit.
I get the most awesome cut with... Onsrud 1/4" SE UPCUT SPIRAL SUPER 0 FLUTE PN: 65-025
Onsrud 63-622's are cheaper and they work too but don't last me quite as long in aluminum. Belin makes a similar.
Watch the chips that are thrown off the whole time you cut. They should look like "little smiles".. not tiny specs and not full piggly tails. When I see smiles, it makes me smile.
I tried cutting fluid, wd40, water, over the years cause i thought I was "supposed" to from reading on the internet. Honestly it never made a difference for me other than to make a big mess of metal shavings in an oily slurry.
But, this is all what works for me.