With BF cabs, I'm now on my 6th. I started with 10's (One10's) and really liked them, then got Two10's and really liked them. Then, for various reasons, I changed to the 12's and was actually disappointed. I thought I was just going to get the same experience, but bigger. I didn't. To me they are really very different. If I were to boil it down, the 10's are old school, rounded, warm and punchy, like a velvet hammer. The 12's are Hifi and reproduce every frequency across the spectrum from huge lows through to faithful top end. It's not what I want. I'm in a blues/rock band playing a P bass with flats, I don't want hifi !
Running the 12's, also required much more diligent choice of amp and eq in order to achieve that sound in my head. With the 10's, most of the work is done already, so more amps sound good with their 10's to me. The GK's have been a revelation though, nothing comes close, even the Bergantino I had, which was super expensive. They are rated at 200w, but with a good BF 4ohm cab, it's more than I ever need.
Would a 400RB and a BF 2x10 cope with a loudish rock band with no PA support? Absolutely! Only the biggest venues would need further reinforcement, but bear in mind, without PA support, it would work, but your backline would be LOUD.
I have recently bought another RB, it's still with my step son in Bristol (he collected it for me), it's an 800RB-II, a classic. When it's back, I'm going to consider parting with my 400RB-III. It won't be expensive, so if you're not sorted by then, perhaps that's something to consider buying until you can find a classic RB-I or II, because those don't crop up very often, and would get you close.