Well, it's ~95% Maris Otter, ~5% Crystal Malt, all Challenger hops, about 38 IBUs, and about 10-11 SRM, per the brewery.
Here's the most current version I brewed:
6 lbs 12.0 oz Pale Malt, Maris Otter (Thomas Fawcett) (3.0 SRM) Grain 5 93.1 %
8.0 oz Crystal Dark - 77L (Crisp) (75.0 SRM) Grain 6 6.9 %
0.50 oz Challenger [8.90 %] - Boil 60.0 min Hop 7 19.5 IBUs
1.00 oz Challenger [8.90 %] - Boil 15.0 min Hop 8 19.4 IBUs
1.00 oz Challenger [8.90 %] - Boil 0.0 min Hop 9 0.0 IBUs
1.0 pkg Burton Ale (White Labs #WLP023) [35.49 ml] Yeast 10 -
Gravity, Alcohol Content and Color
Est Original Gravity: 1.044 SG
Est Final Gravity: 1.011 SG
Estimated Alcohol by Vol: 4.2 %
Bitterness: 38.9 IBUs
Est Color: 8.0 SRM
I usually get a slightly darker color that BeerSmith predicts, and the color is about right (at least as seen in a hydrometer sample), as is the bitterness. The malt character is a little muted, but that may be a factor of age (with a little light oxidation in the bottles I get). The late hop character is also a little strong, but the character is about right, so that may also be a factor of age. I'll know more once I get it out of primary and packaged and aged a little bit. It's in the ballpark, but I wouldn't call it cloned. Next time around I'm going to use a little lighter of a Crystal and use a little more of it, and tone back the later hops.
I tried both the WLP023 Burton Ale (may be their fermentation strain according to internet rumors) and culturing from the bottle. The WLP023 seems closer, so they may be bottling with a different strain than they brew with.
Meanwhile, another round of BJCP studying w/ Weihenstephaner Oktoberfestbier. Seems if you use the 2014 guidelines this is a good example of Festbier, but per the 2008 guidelines it's very out of style as Märzen/Oktoberfest.