Darn close.
I wanted it to capture a similar sound profile, which is why I didn't get the full range Big Twin. The lows are very solid, and not just scooped\subby. There is some meat on them bones.
I'm using a Mesa D800 and was lucky enough to be able to A\B the BF it with a lesser 90s Ampeg 8x10 using the same head. The sound profiles were very similar. I've only been able to use it at full volume twice, but I'm happy so far.
First, all of the frequencies are there. The problem with my GK cabs is that they were missing some of the low mids I was after. The ST is very clear at any volume, without getting brittle in the highs or muddy\farty in the lows. That complete sound helps a lot with your volume.
Second, with my D800 gain @ noon, volume @ 11, Deep off, "passive" mode, Low @ 1:30, Mid-Low @ 1:30, Mid-Hi @ noon, High @ noon I am able to compete with loud drums, a Marshall full stack, and a Randall half stack. When we practice we go full volume. I don't feel like I've pushed it yet.
There are some guys with golden ears and years of experience with 70s SVT gear that will say it isn't in the same league. I can't speak to that. I'd love to hear a V4-B through it.
Tonight when we practice our second guitar player will be out, so I'm gonna go full-on Royal Blood with this thing and see what it does.