The 27" RA cab comes as a 1 x 12 or a 2 x 12. The only difference is the baffle, number of speakers, and the weight.
The RA 1 x 12 comes stock with the mc90 (it's a mesa spec Celestion CL80 with a dust cap and a bigger dust cap). It's a meater sounding speaker which works well for leads and cleans. The tone has more of a low mid emphasis and more of a notch in the high mids which doesn't go well with a Recto, but works far better with the Electra Dyne. It gives the amp a unique but also a really good tone.
Aside from that speaker, you can order the cab with a v30 or their new Fillmore 75 (eminence), which is similar to a v30 but with smoother and less buzzy highs.
The 1 x 12 I have sounds really quite amazing, you would not be disappointed. Orange cabs are cool but I find the buzzy highs to sound weird with mesa amps. Just my opinion. I'd hold onto the Orange cab and get the 1 x 12 extension cab so you have the Electra Dyne head. That way you can run it with a 2 x 12 or a 4 x 12. The 1 x 12 is fantastic for 'loud-ish' bedroom tones and it records well. The Electra Dyne is a LOUD amp and it is punishingly so through a 2 x 12 or a 4 x 12. Just putting that out there.
