A killscreen game with an efficient board-running scheme, decent spring averages, and a lack of conveyor/rivet screwings should push you past 900K. Nearly every game I've played in the past year, where I was running boards and managed to survive beyond Level 12, has been at 920-950K pace.
Wow, 950??
With just top hammer, and no grouping (Ross grouped in his 970 game), it's very hard to average better than 8,700 per barrel screen.
To get 950 pace, you'd have to have a big start (120K+) and beast averages on the other screens (like 8K conveyor, 7K springs, 7K rivets).
If you're routinely pacing 920-950K on (halfway-or-further) top-hammer games, I'm very impressed!
When I am running boards even with good, shit-through-a-goose efficiency, I can't sustain much better than 900-910. Maybe for a few levels, but not deep. It corrects itself eventually.