I have the exact same enlarger as you but with the reverse of your problem. I was used to using a very old Meopta Axomat 1a which gave me 8 seconds for 5x7 and around 20-40 seconds for 8x10 (20x25cm). Switching to the Durst, the 5x7s were lucky to need even 3 seconds and 8x10 were around 10. At any rate, I switched out the globe last week for a 75 watt globe which has slowed things down a tad.

The M600 has a maximum ability to use 150 Watts, so it won't have any trouble if you want to up the wattage of the globe.