ARC ref 75 tubes 120 vs. 150’s?

Guys I borrowed a friends ARC Ref 75 With the KT 150’s installed. Loved the power and definition but the drums on Classic Rock stuff sounded unnatural & shrill on 8 ohms, bit better on 4 ohms but overall prefer the drum sound On my AR VT 100 mk 2. Has anyone heard the AR Ref75 with the 120 tubes? If so how did the sound compare to the 150’s?
i have a ref 75 w kt120 but never ran it with kt150’s

the amp needs an upgrade to run the higher bias kt150 i believe... it is not just plug and play

i also have a vt100-2, w kt88’s... to me the ref 75 is sweeter and more quiet/blacker in background than the vt100 - the vt100 has a little bit of hash in the background, but with twice the output tubes the vt100 definitely provides a bit more drive on dynamic swings - how much treble ’snap’ the vt100 provides is a function of what input tubes you use as well...

Thanks, Which sound do you prefer the VT or Ref 75? 
Separate question, have you heard the AR Ref 210 monoblocks? My buddy has a pair to sell for $8k but I can’t afford them now, just curious how they sound ....thanks