I'm thinking asking the ProAc Response people about this upcoming event ought ot be very enlightening... I'd start there myself.
As much as is the talk hereabouts on the room vs speaker integration, I'm not terribly certain I'd build a room for one sort of loud speaker only.
I'd be far more tempted to errect such a thing for space instead. A room for one? Two? or Six people regularly? That is a consideration too.... as is upgrading speakers later on.
Neither am I too sure there is some 'cast into stone' parameters for exact room size per pr of speakers... or vice versa. I'd suspect there is some latitude for every speaker set with regard to the room it is capable of adapting to.
Volume is the important thing, not just square footage.... then too is the perspective you want while listening to them. Nearfield? Well back?
There's some immense amount of info on what is the perfect room size as it relates to nodes, peaks and dips, from a purely frequency range perspective.
I'd think you'll find only a most general notion as to what is the optimum sized room for most any speaker... but hopefully you'll get the right info as to your needs.