I've messaged the guy at 'acoustic-control' to ask about the RW grade and also if custom panels are available. I'll post back when I have a reply.
WRT acoustic treatment, what you refer to here
Unless the spare bedroom you're referring has walls consisting of 15mm acoustic plasterboard, 4" Acoustic Rockwool insulation, 15mm plywood, 4 " Celletex and dense concrete blocks on all 4 sides!!!
is 'soundproofing' (the expensive part of the job) and won't actually make the room sound
any better, the panels you are about to buy will, and if your experience is like mine, they will make a huge improvement to the room sound.
edit to correct info in previous post :- the ebay seller does not suggest a 50mm spacing just that WRT his supplied hook and eye fixings "Space is left between the wall and your panel to create an air gap which traps additional, unwanted sound."...