The 5881 is the loudest of the bunch and it has the most “marshall” vibe.
If you have a power tube retaining clip on the socket, it will need to be removed for a 5881 to fit, it has a larger base. We tested a lot of tubes including the KT-66 and 5881, they all sound and feel a bit different. So far, the conscience among my tone buddies always comes back to a good 6L6 for the Two Stroke. A good NOS rectifier tube sounds great too.