Mine ended at 19%, FG 1.016. I left it in the primary a little over a week after the readings were steady for two days, and I haven't noticed any ill effects from this. I kegged it Sunday to carb up, and at kegging it was beautifully clear and tasted fantastic. I'm sure it won't hurt to keep it on the yeast as long as you feel comfortable to get it cleaned up.
I racked it last night... and was SHOCKED at the shallow yeast cake. Makes me think there's quite a bit of the 099 still suspended and it was mostly 1056 in the bottom. I literally expected a good gallon of yeast. Ended up racking almost 95% of the pre-ferment volume to secondary into the V-Vessel. Looking like ~4 gallons.
Added about half a bottle (.50oz) of biofine to encourage more settlement. I don't plan on dry hopping for a week or two.
I suspect the following to contribute to the low final gravity:
1. Low, and I mean LOW mash temp. This was a mistake, but it paid off. I mashed around ~145-146 for between 90-120 minutes. Minimized the unfermentables, I assume.
2. Small additions of corn sugar. Kept her hungry. I addded ~2.9oz 3 times a day to a collected wort volume of 4 gallons. 7AM, 1pm, 7PM, until I used an entire 4 lb. bag. Then I stopped...even though she wanted more. Stopped at 1.009-ish. She kept going until 1.0025-ish. What a ho.
3. Never let the actual wort temp climb into the 70's. This was surprisingly easy, since I never had a violent fermentation once. Perhaps because I didn't throw the entire planet's population in yeast into the fermenter. I only pitched the slurry from a 2L 1056 starter (1.040) to get it going. Then I pitched the entire 2L starter of 099 from the actual wort (1.096) 4 days later, but it was COMPLETELY fermented out -- no flask bubbles on stir plate for at least 2 days before pitching.
Hopefully this will help others.