It's going to be personal taste. I found that I didn't like the RA so much through my 2x12 recto, and I LOVE it through the RA2x12 cab. The RA doesn't push a ton of lows, so having a ported cab helps keep it from sounding shrill. I think that the RA cab is a good combination of some of the tight thump of a closed cab and some of the extended bass plus open clean feel of a 3/4 cab.
HOWEVER, I tuned my tone controls after switching from recto 2x12 to RA2x12, and I've never gone back to see how the closed cab sounds.
The RA2x12 combo should sound a lot like with the RA2x12 cab, as it is similar size and ported exactly the same. Take the casters off so you don't lose all the bass. I played a combo once and it sounded a little nasal to me, which I believe is because it was off the ground. Even 3" makes a noticeable difference.
Note, my RA 2x12 has a V30 and a Creamback 75. I really like that combination as the creamback gives more complexity to the mids, which I think complement this amp.
When you play through a RA, remember it's not a Mark. You can turn the gain AND the bass up. I run vintage channel gain and bass at 3:00, mids about 1:30 and treble <11:00. The amp wants to scream rather than thunder, but you can get it to thunder. And scream.
The power attenuators are fantasic for dialing the tone, but I wouldn't rely on them for bedroom volume. I have mine set up with no attenuation on Clean, and -4dB on both Vintage channels. To me, this gives the best tone, plus it allows the clean channel volume to match the vintage channel volume without dirtying up the clean channel. For home use, I run it through a Rock Crusher to drop the overall volume. You can run the internal attenuators down to very low volume, but I had the Rock Crusher already, and that way I don't have to keep messing with the attenuator controls on the back of the amp. Also, I run the masters at >12:00, so that would put a lot of heat into the built-in attenuators, which I would avoid. They can probably take it, but I'm sure it can affect lifetime.
I have already had to change the power tubes, so I know I am pushing them. But they sound so good, I'll be happy to put in a set once a year.
Electra Dyne Head
JP-2C WICKER, Baby!
Mini Rectifier blue LED
Recto 2x12 Horizontal
2x Recto 2x12 Vertical