You are trying to compare apples and oranges. The KT150 tube, "triode strapped" or not, doesn't sound anything like the 300b. I assume that you are considering a 300b SET and not a 300b amp in PP configuration?
There are practical implications beyond the obvious sonic differences: a KT150 amp is going to be PP design, putting out more Wpc and many (most) will allow the use of 4 ohm speakers. Almost all 300b SET amps are going to be 8 Wpc channel or less, and most will provide 8 ohm taps to the speakers. So your speaker selection is going to be critical to the success or your choice of amp.
My suggestions is to choose your speakers first, then find an alp that works and sounds best with your speakers. Doing it the other way is putting the cart before the horse...
There are practical implications beyond the obvious sonic differences: a KT150 amp is going to be PP design, putting out more Wpc and many (most) will allow the use of 4 ohm speakers. Almost all 300b SET amps are going to be 8 Wpc channel or less, and most will provide 8 ohm taps to the speakers. So your speaker selection is going to be critical to the success or your choice of amp.
My suggestions is to choose your speakers first, then find an alp that works and sounds best with your speakers. Doing it the other way is putting the cart before the horse...