Hi guys! What do you recommend as the best speaker mix here?

[D-Rock]

I did some major testing this evening and I actually am finding I don't like mixing speakers! I am hearing some weird unbalanced issues and woofiness. Go back to all the same, and it clears up!

I just yanked the V30/T75 mix out of my 1960A. Mainly because I've decided to sell it. But I wasn't digging the mix anymore after playing my other cabs so much lately.
Now I'm running 4 V30's, 4 V12's, 4 GB's and 2 Vet30's in a 2x12.

Does the Greenback cab handle hard rock, tight lows OK?

Yup it handles hard rock and has tight lows. Although they are G12C Greenbacks, so they differ slightly from the G12M's. They were designed by Celestion for Marshall to be used in the Hendrix cabs, and they ended up putting them in the Vintage Modern cabs too which is what I have. They handle lows better than regular GB's do and are tweaked slightly somewhere in the mids or highend.
I usually use that cab with my 50 watt amps, or I pair it with another cab when running a 120 watt amp.