Flatter shooting....Good bit more retained energy downrange...And as far as cost, they are no more than hornady's other ammo for the 30/30. Or like a dollar more but an insignificant amount nevertheless. Hornady ammo is a little more costly than say the corelocts but you are getting a better bullet. Granted the rem's are great bullets but I personally preferr the Hornady's. the added expence to me is worth it. If I have a Bear commin at me with LUNCH on his mind I want the absolute best I can have in my weapon to insure that Im not gonna be his next meal. Im no Daniel Boon or Davey Crocket and really would rather not try to take on a hungry Bear with ma Knife!!! I hunt alot of Bear country so yes its a concern. But also, like stated above, if the round inspires more confidence then go for it. As long as it lives up to that confidence. Which it so far has. I shoot the new 444xlr which was designed around this new ammo so I personally will shoot the ammo that the weapon was designed around for its maximum performance. Something alot seem to be forgetting is just that. This ammo was designed for the new xlr rifles from Marlin with the 24 inch barrels. Now...Some are gonna say that 2 inches wont make much difference. And if you reload you may be right. Then again you may not be. I did a burn test with mine and found that I am getting JUST at a full burn which translates to optimum performance from the load. So if you are shooting it out of say an 18 inch guide gun barrel you are going to have a good deal of powder burning off after the exiting of the bullet. Now with a 22 inch barrel you may only be losing a grain or 2 of burn which would translate into about 350 to 600 fps and yes 1 grain can make that big of a difference in exiting pressures.
As far as the temperature question I dont know. I dont hunt in such conditions nor will I. I dont feel the need to hunt a MuskOx so I dont think Ill be hunting in 40 below zero temps or more which is what it would take to harden the polymer to any degree whatsoever.