That's actually pretty interesting. A full flavor 3% beer, that you can quaff like no tomorrow! Now that's a lawnmower beer, or snowblower beer if you're from the North!
I remember when I first started brewing, I emailed a brewery in Texas for their Winter Warmer (9%), I mashed what they specified, but way too high, about 165. Ended up at 4% and tasted like jalapenos! Seriously.
I've heard that darker malts can't get too low a FG...My latest black ipa (mashed at 149 for 90 mins.) had a pound of Caraffa III in there, with a pound of sugar and used US-05, only got down to 1.016. Not certain about the dark roasted malts, just something I've read. My lighter IPAs with the same amount of sugar and same yeast get down to a nice dry 1.010.