I’m very far from an expert but… you’re writing about wanting to carve and do butters like Knapton, so why not just do as Knapton does and go for a Donek Knapton Twin? According to the donek website they can be customized both flex and width wise to suit the rider

You also have the Exegi Double Wide available in the store here, waist width of 288 mm in the regular width. But I’m guessing that’s more of a pure carving board that may not be suitable to butter on. 

There are also quite a few volume shifted boards with waist widths around 275, but that’s not much wider than what you already have 

Bindings I’ve got no clue. But I think James really likes the Flow NX2 for how little they add to the length of the boot (basically zero extra length) and they’re also quite stiff and responsive which helps. 

Some of the Asian carving sorta fits between Cherry & Knapton... often posi, but with some freestyle tricks thrown in.  Their boards are generally too narrow though.

Where are you located?  You might check to see how wide Exegi could go.  Donek is also an option, and there's probably a few places in Europe.

Thanks @superfelix, that's quite correct.

Donek makes the widest boards but not the best boards.  If you like buttering and you ride a lot of switch the Knapton Twin is a good option, but for high speed caving it won't hold enough edge pressure.

The Exegi DoubleWide is available in the store now, 294mm is the standard waist width (the 288 is the skinny version).  You can also customize your flex if the butters are important, but realistically you won't find a board that's simultaneously great for butters (soft flex) and great for high speed carving (stiff flex).  My solution is just to own a lot of different boards...

I do have a four JJA snowboards for sale right now.  I'm sending a mass email to the waitlist tonight (or tomorrow).  To get on that list put your email in the "Notify Me" box here: https://carversconnection.com/product/jasey-jay-working-title-snowboards-copy-2/

And yeah, any Flow binding will reduce the amount of boot drag you experience because there's no heelcup with the Flow design.  You'll end up taking about 1.5cm or more out of the total length (boot plus binding) over those Union Atlas, which is the equivalent of adding that 1.5cm to your waist width.

Risers are a good option too for reducing boot out and increasing your leverage over your edge.  I expect them to be available for sale in the store by end of day tomorrow.

Either way, that Otto is way too small for you and it's designed as a freestyle/park board too.