If you do go for a slow speed-up on the spindle and let the G-code start it just before the cutting begins you may need to add a delay to let it come up to speed. I've found this necessary using CamBam and LinuxCNC (though I cannot remember exacltly what my acceleration setting is, I'm sure I took the advice on this forum). I manualy add a line 'G4 P6' just after the spindle start line to add a 6 second delay.