I'm looking at getting a second 4x12 cabinet that would give me a different sound than the v30's in my Mesa traditional. I really enjoy my v30's with the Invader, however I've heard that the Invader is an amazing amp for pushing two 4x12's, so I was thinking of having two cabs in my live set up, I'll of course keep the Mesa 4x12 w/v30s, but I was wondering if you guys had any suggestions for a second cab that would be an interesting mix with the v30's.

At the moment I've been looking at VHT/Fryette Fat Bottom 4x12 with the P-50-E speakers, I was wondering if any one that has this cab, or have heard it used in a set up, if you could compare them to v30's at all, or even describe its type of speaker in terms of low end, high/low mids, cutting through...etc

I'd also like any other suggestions you'd have for a 2nd cab, something loaded with anything but v30's.

Thanks in advance, have a good one!
Main rig:
ESP Horizon FR-II
ENGL Invader 150
Mesa Traditional cab w/ v30's
ISP Decimator Pro Rack G
BBE Sonic Maximizer 482i

Back up rig:
ESP Eclipse STBC
LTD EC-1000 VB
Framus Cobra modded
Well, You'll have to consider cabinet impedance first. Your Mesa is 8 ohms mono, so you will need another 8 ohm mono cab in order to run both in parallel. (unless your ENGL allows for, and has multiple external jacks with varied impedance options)

As for 8 ohm mono 4x12's, look into Randall XL, Framus Cobra, Engl Standard.
MESA 412