Caliber doesn't make any difference as to whether the barrel's throats are properly cut. A faulty/dull reamer can cause an improperly cut throat, and that can happen to any rifle in any caliber. Especially a rifle that was factory chambered in mass quantities (regardless of brand).
As for "properly finished", I am not aware of any factory rifle barrel that will have a polished throat when it leaves the factory, unless it is a custom shop rifle and the barrel was hand-lapped. That's what breaking in a barrel, and/or hand-lapping a barrel does, it polishes and smooths out the imperfections from the machining processes to drill and rifle the bore. That dealer obviously has no idea what he's talking about.
And as many rifles as Remington produces, if one run of rifles in a particular caliber DID have a bad throat in it, that reamer that was used to cut those chambers is most likely LONG gone by now.
As for the action screws, I use factory Remington action screws, and have had zero problems.
As for the caliber, that "nice dealer" sounds like a supporter, and just wanted to sell you a bigger caliber to sell you more expensive ammo, and more powder (RUM's use ALOT more powder than a 7mmRM), etc... Not to mention all that smoke he was blowing was most-likely just to get you to buy his favorite caliber.
