How do tube manufacturers like VAC get 55 watts per KT88 where others get only 30-35?

Just wondering how some push pull tube manufacturers like VAC and others get 55 watts per KT88 tube while others are more in the range of 35? Does driving a tube hard like this have any ramifications as to distortion, sound, headroom and tube life? I know VAC amps are highly musical so design, power supply and output transformers obviously contribute much to overall sonics. A company like Zesto gets about 25 watts per KT88 but uses a class A push pull circuit rather than class AB.  This seems like an attractive design.
I guess, as always, it's all in the implementation. Thank you for helping me to better understand.


Didn't know if you were still interested in the VAC 200 IQ, but one just one up on audiomart at a great deal.  Any updates?  Keep us posted.
I've heard the 200 iq and it is pretty amazing - the clarity, transparency yet body and realism that Kevin Hayes gets out of that design is mind boggling. The flexibility of tube rolling with the auto bias does make it one of the most user friendly amps on the market.
I've heard the VAC 200 IQ with Sonus Faber, Magico, and Focal and drives them all equally well.  Doesn't seem the VAC are speaker dependent at all. At 100+ watts, any speaker will work well down the road, which is always nice to not be limited in the future in case you change out speakers.