Aside from gathering data from prior batches, what is the best way to try and estimate final gravity when planning out a beer?

I know from experience that some of Wyeast's strains are far more attenuative than their fact sheets imply, so simply using their attenuation percentages doesn't work. Clearly mash temps factor into all this as well.

What's driving this question are the two beers I've got fermenting right now. Brewed a 10g batch of best bitter on Sunday, split it into two carboys and pitched Wyeast 1968 in one, 1318 in the other. Right now the 1318 is at 1.014, while the 1968 is at 1.011. I'm hoping they both finish in the mid-upper single digits for FG, and it occurred to me that I don't have any real idea what to expect them to finish at.

Mash was 152 for 90 minutes, final temp was 149, FWIW. 93% MO, 5% Crystal 60L, 2% Chocolate.