I decided to go directly to the source and I was rewarded with this delightfully imprecise reply from one of Fuller's brewing managers:
"Thank you for your e mail and we are pleased to hear that you have a bottle of our 2005 Vintage which you are looking forward to trying. As to when is best to enjoy this beer is to some extent down to personal preference. As all of our Vintages age they take on and emphasis different facets of their complex flavour. The older Vintages acquire deeper almost sherry like notes they also become a deeper colour. The 2005 when I last tried it had certainly developed these and had almost dark cherry chocolate finish.
"Last October we held a vertical tasting here at the brewery inviting a number of beer writers and experts to comment on the 15 years of Vintage to date some of their comments can be found on their web and blog sites.
"My own personal preference is for the slightly younger Vintages and I am particulary enjoying the 2010 and the 2011 but a number of my colleagues and those at the tasting above prefer the more complex older ones. My slightly tongue in cheek advice is to try your 2005 now at a suitable occasion if you feel that you would prefer a little older I believe that we still have some 2005 available from our shop then you should be able to acquire another."
Of course it wouldn't be fair to expect marching orders but on the other hand, I'm still not sure what to do. I hear tell I could flog that 2005, not to mention my 2007, for a pretty penny.