Aluminum SFM upper limits?

Hi,

What are the upper limits for surface speed in aluminum? Harvey tool general recommendations are 1500 SFM. I'm looking at using a 24k rpm spindle with 1/2" or 12 mm cutter, which would generate about 2740 SFM at 21-22k rpm. This is way past the recommendations, but must be in the realm of or even much smaller than what Datron machines would run given their spindles. Any thoughts?

This is actually a spindle selection question; I'm trying to decide between a constant power spindle with 12k rpm at peak power and a constant torque spindle with peak power at 24k rpm. The 24k rpm is much better for the smaller tools I'll use a lot, but just want to make sure that it will be OK for roughing with a 1/2" end mill, too. Context is a quite rigid fixed gantry router.

Thanks in advance. I can read charts all day but still don't know anything about the practical application ;)

Also I know I've been posting here and there all over the forum- I'm super close to starting a machine build thread, just gathering a bit more information first!