Re: 280 Rem??
I've used a .280 for the last 15 years, and I have to say, I think it may be the best deer cartridge around. Yes, the .30-06 can do all, but the .280 shoots flatter than the .30-06 and .270 (with equal weight bullets due to it's slighlty longer case and capacity), it has a great deal of bullet choices (if handloading), is easy on the shoulder, and can be easily made into an Ackley!
I don't have experience with the X-Bolt, but I did do some shooting and loading for a friend for his A-Bolt in .280. It was a very light rifle and it shot very well. It actually shot my handloads for my Ruger better in his gun! I'm not a huge Browning bolt fan, but they are a decent gun. Their BARs and shotguns are nice though...