I ended up getting a pair of STR-441 and a pair of STR-445. Here's a comparison I did:
Mesa/Boogie 6L6GC power tube comparison. Mark V on 90W, ch 3 Mk IV mode. EMG 81X, drop-C. EQ in the loop. Recorded direct from the slave out into a mix of 5 IRs (per channel, double-tracked stereo) I made of my speakers (MC-90 + V30 left, Jensen Tornado Stealth 80 + V30 right).
The only thing that changes is the power tubes. A rimshot indicates a tube change. Order is:
1: 4 STR-440
2: Inner 2 STR-441, Outer 2 STR-445
3: Inner 2 STR-445, Outer 2 STR-441
4: Inner 2 STR-441, Outer 2 STR-440
5: Inner 2 STR-440, Outer 2 STR-441
6: Inner 2 STR-445, Outer 2 STR-440
7: Inner 2 STR-440, Outer 2 STR-445
I think the biggest difference is between the first two.