I used blackstrap molasses and I can definitely pick up a bit of residual molasses flavor. I also get a bit of smoky/bacon notes from it as well, but it's not too overpowering. I'm also wondering if the minerals in my water profile are accentuating that a bit.
That's a good point about the FG that I hadn't considered. The Yorkshire Square yeast is definitely more attenuative than I had expected. I went from 1.059 - 1.011 on this brew. Seeing as it's so ridiculously flocculant, I was assuming I'd end up a few points higher than that, despite the added sugar. Although Old Pec doesn't taste sweet to me it definitely has a fuller, rounder malt character than my brew.
As is the case with most of my clone attempts, I will definitely make some changes to my recipe the next time around, although not necessarily to get closer to the commercial brew. In my first pass at cloning a brew I almost always find some differences from the commercial beer that I enjoy in my own version. In this case, it was definitely the molasses. That flavor just works so well in this beer, even though it's definitely different from the commercial brew.
Changes for my next rebrew:
-Use all molasses for the sugar addition. I'm thinking of cutting the blackstrap amount in half to cut down on the bacon, and replacing the Lyle's and the rest of the blackstrap with regular dark molasses.
-Use a softer water profile. I'm leaning towards the ballpark of the London Pale profile from Martin's Zymurgy article
In other words, I'm leaning more towards a London ESB with molasses than a true Old Pec clone. I can get my hands on OP pretty easily, so I'd rather brew something inspired by it with my own twist on it.