Having 6ohm speakers the ability to switch between operating points is like having two amps in one.
Tube rolling is like having a
collection of different amps in one pair of monos without any of the hassles of lifting and storing. The best part is, you can go back to the factory sound anytime you like.
I am now using Valvo 7308s. I've used others in the past.
Mullard e88cc - Golden glow, classic tube sound
Mullard cv2492 - more spacious and linear but still warmer than stock
Telefunken CCa Red Tips - extremely quiet tubes, very refined, very extended and clear with a touch of sweetness but not as full bodied. The choice for detail oriented types of listeners or those turned on most by soundstaging.
The Valvo tubes which were made in the Amperex Holland plant are somewhere between the CV2492 and the CCa reds. Soundstage is a bit shorter but there is more texture on strings, vocals and brass.