Tyll,
I think it is great that you took all that time to both build the kit and do the comparison. Not to mention that the video will be a great help our newbies (to kits). I started on kits in 1965. What a piece of crap that was!
Breaking it in for 30 hours will get you a goodly percentage of break in. Paul Joppa and Dan suggest that most will happen by 100 hours. Of course the tubes used also have a lot to do with the sound character as well. Since the driver tubes were not the same you couldn't have just swapped the tubes to keep that on a level keel.
Sorry, I'm an engineer so I wonder about one to one comparisons. It is a sickness but I haven't found a treatment.
Again, I am happy to have this link on the site for guys who don't know how to solder. That, and your advice, will be a boon to Bottlehead.