Couple things going on here.
You're feedrate is way too low. I'd double it, but I wouldn't try to cut so deep in one pass. With bits smaller than 6mm, I don't like to cut much deeper than the tool diameter with each pass.
The burning is from all the chips packed in the cut. You'll never get the chips out of the slot with a 4mm bit. Even with a 6mm bit, you'll have a difficult time getting the chips out.
10mm or 12mm compression bits.I can't understand how the cabinetmaker workshops do it - they seem to be able to cut through 16mm dense laminated board in one fast cut. What sort of cutters do they use?
One pass, 16,000 rpm, and 15,000-20,000 mm/min. 10HP or bigger spindles
This requires a lot more machine than you have, though.