The longer you lager it, the better. I had one of the precious few bottles that remain from this batch about a week ago and it is really fantastic. Scored a solid 41 in a recent competition. It is aging extremely well. Very different (better) beer than it was 8 months ago.
I will be doing my next batch of this soon and will be making a couple of changes: mash schedule 122 (protein), 149, 160, 170. A bit of carapils to help head retention. Hallertau Mittelfrueh for hops. A small (SMALL) flavour hop addition very late or at flameout (maybe Tettnang). Cut the chocolate malt back to 2 oz. I was going to repitch 2308 to ferment it but may go with 2206 and a big starter.
I hope yours turns out as well as mine did. I really like this beer. If you become serious about this style pick up "Bock" by Darryl Richman, part of the Brewing Classic Styles series. Everything you need to know!
I encourage Bock brewers to try at least one decoction, but be warned, the volume can be really difficult to get right!
2012 Canadian Brewer of the Year