I spent a couple of hours test-driving Mesas today. I tried the Rect-o-Verb combo, and both a Dual Recto head and a Rect-o-Verb head through a Mesa Recto 2x12 cab.
The Rect-o-Verb combo is ridiculously loud for a 1x12 50W combo. Heavy and very bell-like, but not quite what i was looking for, so i plugged into the Dual Recto head and 2x12 cab. Absolutely awesome. I spent a fair bit of time with it, but since i don't really want or need a 100W 3-channel amp, i pulled down the Rect-o-Verb head and plugged it into the 2x12, which is closer to the rig i'm now seriously considering. (Like you, i'm looking at getting a Solo 50 head, but i'm only looking at pushing a 2x12 cab for now... i don't think a 4x12 would fit in the back of my Golf. If i need to move more air onstage, i can always add another 2x12 or rent a 4x12.)
I spent a lot of time tweaking and playing with the two channels and five voicing settings. Got a really amazing clean sound with the Clean voice in channel 1. Really deep and lush, with a nice bit of spank to it. The Pushed voicing was really awesome as well... it made the harmonics just jump off the fretboard. It was a bit more edgy, with more cut and more upper mids, but still authoritative and balanced.
In channel 2, you have Raw, Vintage and Modern voicings. There's a fair amount of overlap between each of these. Raw will go from grit to a pretty good grind. Vintage will go from mild grind to pretty wild. Modern is nuts. I found that after tweaking the gain to get approximately the same sound, each of the voices was progressively "tighter" sounding.
I found that in Raw mode, with the gain all the way up, you can actually get a pretty decent amount of punch, and really nice distortion, with a slightly loose feel. Switch to Vintage and roll back the gain to about 2/3, and you get a similar amount of distortion and punch, but with a much tighter feel. Pushing the gain a bit more gets you back up in to serious grind territory. When i switched into Modern mode, anything in the store that wasn't screwed down tight started to rattle. Above 2/3 gain, the saturation just got too harsh and buzzy for me. Backing it off to about 40% or so again gave similar amounts of gain to the sweet spot i found on the other two voicings, but it was tighter and louder than both the Raw and Vintage modes. Being primarily a rhythm player, i found the Modern voicing to be a little too harsh for my ears, but for some, it may be just the ticket.
One thing that totally blew me away with the Rect-o-Verb head was how sensitive it was to pick nuances and the differences between pickups. I took my Duncan-equipped Dean 7-string with me to audition the amps. The Mesa really let all the character of the neck '59 and bridge JB shine through. And the amp preserved all the sparkle and twang when i switched the pickups into parallel mode. The Rivera S160 i tried earlier in the day didn't accomplish this in its gain channel... no matter what i did, it sounded the same. It had a spectacular clean channel, but the gain channel just didn't do it for me.
I was very impressed with the Rect-o-Verb head, and the Recto 2x12 cabinet just kicks. The Dual Recto is nice with its additional tube rectifier section and bold/spongy variac control, but was really more amp (and more $) than i need.