I have used a Ryeland tup on Mules and other large ewes, merely because I had one along with my pedigree Ryeland ewes, and the Ryeland Sheep Society said what a wonderful terminal sire the Ryeland was.
I didn't do it again, as although I got perfectly acceptable lambs, they didn't make the weights you get from a Suffolk or a continental ram.
So, as you've got a Charollais, I would definitely use it. There's no point in using a smaller ram and ending up with smaller lambs.