End Mill Types for Aluminum

[Cartierusm]

OK, so I usually use whatever bits I can get on sale. I cut a lot of 6061 Aluminum on my converted BP. Because of the steppers on my conversion I can really only run 15 IPM and .25" Deep with a 1/2" End Mill at 3000 RPM with mist coolant.

So first question if I can only go 15 IPM 1/4" deep with a 1/2" HSS or M42 End Mill should I still be running at 3000 RPM?

Next question what out of the listed below would be the best bang for the buck taking into consideration cut quality and tool life? These are cheap imports. I'm not sure if HSS or one of the cobalts are better for Aluminum or is Carbide?

1/2" 2 Flute HSS $2.76
1/2" 2 FLute M42 $7.30
1/2" 2 Flute M2AL $4.70
1/2" 2 Flute Solid Carbide $23.00

[BarnBurner]

I only machine aluminum, and have settled on solid carbide, uncoated. And although mist coolant works okay, the mess it leaves when the water evaporates can seize a machine.

I use WD-40, and don't even need too much. Either spray before cutting, or set up a drip, like an Intravaneaous <sp?> bag.