Hi Andrew,
The big surprise for me this year was that the white ones ended up noticably smaller than the bronze. Also, we fed ours ad-lib pellets, and I think they reached full weight sometime in November!! The bronze hens (we only have girls unfortunately) have ended up at 6kg ish dressed, and the white just over 5kg. The bronze are much harder to pluck though, given all the dark fluffy bits!
I'm not sure yet if we'll have any next year (Mrs Womble says yes, but then it's not her who has to do the difficult bit at the end!!). However, if we did, I think I'd go for bronze, basically just because they're prettier, heavier, and when sold still seem to command a premium.
Thanks again for organizing - we're looking forward to our Christmas dinner now!!