In general, in a standard single ended "300B" amp, assuming that everything is reasonably done, the things that influence the overall sound from most important to least important are ...
1. topology (including the power supply)
2. quality of passives and iron
3. quality of driver tubes
4. the 300B's
Western Electrics may well sound a lot better than Valve Arts, but I'd take a well designed amp with good iron and caps and cheap tubes over a run of the mill amp with WE outputs any day. As a matter of fact, I have 300b amps with good iron, a good topology, and extra cheap tubes. They sound great.