The WSMs are all based on the same case. The calibers that have been produced so far are the 270, 7mm, 300, and 325. I believe the 325 is the least popular - that's not because it isn't a good round. The others are flatter-shooting. I currently own a 270 and 300. They will both shoot way out there, and I don't think 500 yards is out of the question. PROVIDED that the hunter has practiced at that range. As for your gun shop owner saying that he shoots regularly at 600 with the 325WSM, he's either a hell-of-a-good shot or he just happens to have a 325 that he wants to sell you. I live and hunt in elk and deer country. Last week, while I was elk hunting, I just happened to run into a great whitetail buck. Too bad for him. I was using my 300WSM and I dropped him at about 50 yards, but would have felt confident if it had been 450 yards - even if it had been a bull elk. I believe the 300WSM is the best of the WSMs for elk because it is very flat-shooting and has more than enough power to kill a big animal like an elk at long range. Keep in mind that the type of bullet that you shoot also has a big effect on accuracy and killing ability especially when you are considering shots over 300 yards.