Yeah, its def easy to hear after going from a brighter amp like a Marshall, Wizard or a Mesa Mark to the VH4, much less top end. I believe thats the inherent tuning of the circuit from Peters ears, he doesn't like too much high end sizzle in an amp. Blended with those other amps it's a great fit and I can see why Jones and Hetfield do it. The Hagen is less compressed and more open on its own.
I've got Gold Lion KT77's in one and 6L6's in another. I feel I can get closer to a crisper top end with the 6L6's than the KT77's, nothing new there but I can confirm for myself that's what hear. If I had the choice now I'd prob just stick to 6L6's in the VH4. I've read that 6550's are fantastic by many accounts, but not recommended by Peter to run.
I love running the VH4 and my MCII at hefty volumes, but I soon need an ear break. Running the Marshall Super Lead and two VH4's, with one VH4 out of phase wrt to the other is unreal too. Swapping in a dual recto into a VH4 spot is another great one.