Tweaking my Cronus Magnum Tubes

I'm wanting to tube roll on my Cronus Magnum. I have the KT 120's and the standard small tubes that came with the Magnum.Also have the KT 90's. Should I update the KT 120's to Gold Lion 66,77 or 88's There's a quad of Gold Lion 66's on sale here at Audiogon.

W#hat are good small tubes to update and what small tube position are most important to update?

Thanks mates!