I've owned both of the cabs in question. The Carvin wasn't bad but the SVT810E responded
much better to my SVT-VR. The 810E that I bought had some phase issues (it was used and was likely mixed up when the cab was redone in bed liner) but as soon as I fixed the wiring, it sounded phenomenal.
The Carvin is lighter, ported, and has a tweeter. Despite the big weight difference, I didn't find it to be any easier to move than the Ampeg. The Ampeg comes equipped with the necessary hardware to make transport easier (the towel bar is nice and the skid rails are a lifesaver).
I am glad that I made the switch. The BR810 had a well rounded tone but the sealed nature of the SVT810E just rocks with the tube amp; it sounds so forward. Everything feels like a slap in the face and a punch in the gut. There was someone that mentioned how he loved how his tube amp helped form a bridge between the notes his fingers were playing and the sound coming from the cabinet. It wasn't until I used the Ampeg that I felt that connection. It's hard to explain but I can recall the exhilaration quite well. It's something that you have to feel to understand, perhaps. There is
nothing quite like an SVT through an SVT810 paired with a quality Jazz bass sporting a fresh set of light gauge rounds.
I don't want to deter you, or anyone else, from considering the Carvin. There are a lot of great applications for that cab -- it was tremendous when paired with a B1500, for instance. It's a great cab being offered by a great company (I love Carvin's amps). One thing to consider, however, is that a used SVT810E will likely be cheaper than the Carvin.
Either way, I'm sure you won't be too disappointed. Personally, I'd give the nod to the Ampeg. As mentioned previously, a used SVT810 will still be worth about what you paid for it should you decide to flip it. The Carvin, on the other hand, takes a big hit in resale value (unless you find one used). I've never been one to buy something based on resale value but it definitely is something to consider.