Interesting observations. I am looking to juice teh additional 60 watts (per channel) from the 305s to help them deal with the big room. Sounds like it may not be a recommended move.
Pepe
I was running the KT88z Black Beauties in my set of Cherry 180's
I changed them to KT120's and loved the result, went from 180 wpc to 260 wpc.
When I sold my Cherry's to Tinpan he told me that he was going to remove the KT120's and go back to the KT88's
After receiving the amp's and listing to the KT120's he decided to stay with the KT120's
I like the sound of the KT120's I ended up purchasing 30 of them for my set of Silver Sevens approx. 700 wpc
Its 105 watts per channel increase in your set of VTA305's not 60 watts, running the KT88's in a 305 amp
gives you around 200 watts per channel.
Brian