I can vouch for what elvis is saying. I just picked up the Mark V 25 and a mini rec slant 1x12 cab. It sounds great, but not huge. In fact, I'm a little on the disappointed side as in that it sounds about as big as it looks. I guess I expected a little bigger sound. Keep in mind, that doesn't mean that it doesn't sound GREAT, just not huge.
I think I'm going to list the 1x12 on craigslist and holdout for a vertical 2x12. The size of the head begs for a vertical 2x12 or two 1x12 stacked. By the time you get 2 Boogie 1x12s, you almost could have bought a Mini Rec haha. Just makes more sense monetarily to get a 2x12.
I'd LOVE to see Boogie take there Rectifier 2x12 cabs and rotate the logo for vertical use....that would be awesome.