Well, that was an interesting journey. Thank you all who walked with me. As is the BC way, I got sucked into a vortex and managed to borrow 3 sets of monitors, topping out at a £2.6K pair. Once everything was Sonorworks'd it seems that my old HiFi B&W boxes are (for my purposes), just fine and dandy. Were the £2.6K boxes nicer? Yes, of course they were. Significantly better in a way that changed everything from black and white into colour? No.
So there we have it.