I wouldn’t recommend running over 10krpm just for the longevity of the spindle.
This is about optimizing chip-load and thermal transport away from the tool, so that you don’t get heat build-up in the tool or remaining plastic (leading to gluing you’re experiencing). I’ve posted a bit about this on this thread and given further details there, but the important part for you here:
The equation for chip-loading:
Chip Load = feed rate ( ipm ) ÷ ( cutting rpm x number of cutting edges )
that works out like this to solve for feed rate instead:
chip load x rpm x cutting edges = feed rate
According to PDS Spindle’s feeds/speeds chart here, the recommended chip-load for acrylic for a 1/8" tool, which would be 3.175mm, is 0.003-0.005" per-tooth which on a two-flute tool at 5krpm would be 30-50 inches per minute, or 762-1270mm/min.
Therefore yes, even though your tool is a 2mm tool, it’s likely that you’re running the tool too fast against the material relative to the feed-rate, so it’s rubbing the plastic more than cutting it.
Onsrud makes a series of plastic-oriented tools that you might be interested in: the 63-700 series here in their catalog which has an “O-flute” design to improve chip clearing to prevent the bonding you’re getting. They also have a bunch of different feeds & speeds tables available, but you’ll want the hard-plastics chip-loading chart. That specifies a chip-load of 0.002-0.004" with a 1/16" diameter cutter, which is a bit smaller than your 2mm cutter (it’s ~1.6mm), so ~770mm/min is probably a good “middle ground” feed-rate to try at 5krpm, and see how that goes at up to 1x diameter depth cuts.
Or, if we’re concerned that might still be too much heat or lateral load on things, you could go down to 3krpm, and then try a feed-rate of 18ipm, or ~460mm/min.