Old thread, love it. I hate to point fingers as I'm a guitar player too, but unless the drums drown out the bass, it's a guitar issue.
For small gigs and rehearsals I use my Ampeg b100R, never at full volume, competing against 2 guitars - a jcm800 2x12 cab and 59' Fender Bassman reissue and synths. As much as I love my svt and berg 2x15, I rarely "need" it. My thoughts on the mix are always to get the drums and bass in line, and the guitar comes in last and needs to be sure it's in line and not drowning. If it is...buy an attenuator or a smaller wattage amp. (My Dr.Z Maz18 NR is dreamy)
In my experience, I've yet to jam with a guy using a Fender Twin that could keep it tamed. Certainly can be done, just never pleasant times from my history.