I wouldn't have guessed it, but it appears that the Rose and Goat is about 200 feet higher than Mt. Wachusett. Depends on what you count as an orienteering map, of course; there's an excellent hiking map of Mt. Greylock made by Pat Dunlavey, but I dont know that anyone has ever put out controls there (other than on the Greylock Glen ski-O map, which I don't think went that high. But there's also the ISOM (or close to it) Hopkins Forest map, by Platt/Dunlavey, in the NW corner of Williamstown, which I believe does get about 100 feet higher than the Rose and Goat, and which was once considered as a Billygoat venue. I don't know if that's ever had controls on it or not, possibly at some Williams College event.
Should one automatically assume that "highest" refers to the highest point and not the highest average elevation over the whole map, or even the highest lowest point? I think most people would say that Colorado was higher than California. And in this case, I think R&G clearly gets the nod.
And R&G has certainly had an event. And controls. And with inspired course setting could certainly host a Billygoat...
Yes, I was going to mention that "highest" was not rigorously defined. Though the others could easily be converted to "higher" maps by other criteria by the simple application of scissors.