Having said that, all of them are still grainy and if experienced users can't avoid that then I'm certainly doomed.

You're not doomed at all, with a progressive renderer just giving it more time to cook should get rid of the grain. I just stopped mine when I thought the grain looked about the same as BB's. Compare the ceilings or the white ball on the left - they're not that far off - not so far that a comparison cannot be drawn, as shvrdvid is implying.