I went through the same thought process when i named mine as well, but felt it should stay the same cause everyone knew the car, even though the power went up! Also, it did'nt sound right for some reason in changing it 'UK600', 'UK700'... 'UK500' had a nice ring to it, dunno why. Many a time someone came up to me and said "never knew they made a UK500". lol
In John's case everyone will have known it as JW340 for some time cause of the history of the car and the person, but i'd be inclined to keep as is, or think of something original, so that it can stay with it no matter what state of tune.