Well, true enough, but when I used Overheat+Power Swap Ninetales I was able to one on one beat most Volcarona by stealing their boosts even with max HP and Speed EVs, so presumably the same would apply for CMers, though actually doing the calcs is absurdly complicated.. Some extra SpD may help in absorbing the odd HP Rock from a Volcarona as you say, but the insurance of being able to beat Excadrill is something I wouldn't give up.i usually count on tyranitar being dead early, but yes in the sand he is an issue. That being said, he doesn't set up too easily on something that wont put him into nape revenge range. even iron head from durant does a fair amount to him. Overall outspeeding excadrill is probably the better option, but I just love how ninetails destroys cm users and quiver dancers with the bulk she has.
EDIT: Also, very sad that you don't seem to be able to Luvdisc RMTs :(