Ian,
Derek's scale over at Watford is very precise, and really breaks things down to a precise value, so a few points difference on his scale is still so much closer than one can imagine, its scary.
I don't remember what his point spread is on what he considers a "balanced" valve, but the closer is always better.
I would probably use the 250/252 in the phase inverter position, as here we are generally looking for current drive more than voltage gain, and frankly, a 99.2% match is pretty darn close!
All these tubes (valves) are so close, that moving them around, even in V1, or the first gain stage, is probably not going to be a perceived difference. If you want to try something different down the road, then perhaps try in V1 one of his valves in the 190 or so range. That will drop gain in the front end a lot and give you a lot more headroom, if you have a need for a clean sound for a particular situation.
The "problem" with Watford Valves, is you do get, and you do know, what you have in your hands, so at times its can be more tempting to buy two or three tubes from them when you initially only wanted to replace a single bad one
Regards, Thaks Myles, always informative
