As of 2019, Ribcor EE is CCM's widest, deepest out of the box skate. Conversely, Ribcor D is CCM's narrowest out of the box skate. The reasoning is that Ribcor construction is uniquely suited to molding and will serve a customer on the narrow (with D) and wide (with EE) part of the spectrum equally well. The main difference (and this is true for all CCM skates) is that the quarter material is super reactive to heat. So while the Rib EE may seem similar out of the box in size to a competing product, the amount that it will change during a baking/molding process is significantly greater and can fit a lot more feet as a result. Rib EE ends up being CCM's largest and blankest canvas for a foot to fit into and that's what makes it so useful for those with significantly different than stock sized/shaped feet.
Volume is a little challenging regarding Ribcor because of these same molding properties; the amount of wrap is going to depend on a lot of factors including the unique geometry of each foot and the only way to know for sure is to heat one up and tie it. CCM skates can be rebaked multiple times so no need to worry if it requires a couple molds, just keep 24 hours between heatings.
Finally, all CCM skates come with a 90 day satisfaction guarantee so if it ends up not working out, just return the skates and get something different.
As a PS: We've done hundreds of retail fittings since the intro of the new Rib EE and 1 important learning has been that if it seems like nothing will fit well, Ribcor will probably end up working... Oftentimes we'll get called by dealers or equipment managers to work out an especially difficult fitting scenario and more often than not, the result is a Ribcor construction.
Good luck with your skate search!