Probably not worth unless you have the xtra cash and just like messing with wildcats like that. The sharper shoulder angle would be nice.
Several years ago I designed, in conjunction with Dave Kiff at PTG,what I called the 300 RUMBO. I believe it was Autorotate here on lrh.com that bought the reamer and go gauge from me as I had decided to go to a 338 Lap Imp, the 338AX, specifically, instead. The 300 RUMBO absolutely maxed out the 300 RUM case, more than the Tomahawk even, but again, probably not enough to make a meaningful difference, unless you just like messing with wildcats. Autorotate built a rifle around the 300RUMBO, but his smith didn't fully get the max out of the case by not inserting the reamer are far is it should go so that a guy could still shoot a standard 300RUM case out of the rifle. So unless someone else actually fully utilizes that case capacity by building another rifle and using the reamer as it was designed, the capabilites of the design won't be known, but it won't be anything earth shattering. Autorotate was trying to sell his dies, reamer, etc. for the 300RUMBO some time ago.