Overall, unless price is the hang up, I would go with just about anyone else than BCA. Their track record with quality on their packs these days just sucks. I've seen their new packs and they look nice enough, but I don't know that they will hold up. Blown stitching that sort of thing. Their warranty department is good and they'll fix 'em, but who wants to deal with that?
The versatility thing. It's nice to have, but I wouldn't make that a deal breaker. You want to buy the pack that you are going to use. I that for over 90% of my bc endeavors, I am going to use one pack. Generally speaking. As far as for cross sport use. I also find that I usually go to something different that is more specific for what I am doing. Again that's me. Plus if you are going to drop that sort of coin on an airbag pack, do you really want to put wear and tear on the pack for other pursuits? Making it wear out quicker?
If you can, go try on the packs you are interested in. The MR pack may weigh more but it may also carry a ton better. Load it up and try it on. If it carries better, it's worth the extra pound of weight. I know that is a really key thing about the Mammut packs. They carry their loads quite well.