Installed the 9020 last night, switched it on and it bagan to make beautiful bubbles right away. Still need to fix a waste collector tank somewhere - for now the two tubes are just flowing into a 2liter ice-cream tub resting on the baffles. Already some dark-green gunk in there this morning.
So, I've upgraded my skimmer from a 9010, to a great-condition second-hand 9020, doubling my capacity. The 9010 is rated for 1000liter and the 9020 is rated for 2000liters. I have about 850liter, some of which are liverock, so this should be just great!
Thanks RaveMan!