I shot a 7mm/08 out of a Remington Mountain Rifle for about ten years. In the last three years, I have been dabbling with a .257 Roberts.
What I have found is that there is very little difference. They are both very efficient deer cartridges, and kill very well. I have only used the 90 grain Sierra BTHP, the 100 grain Hornady and the 110 grain Accubond out of the Roberts, I would use the Sierra again if I had to, but would prefer the others if possible.
In the 7mm/08, I have used the 120 grain Sierra PH, the 140 grain Nosler BT a great deal, the 139 grain Hornday interlock, the 130 grain Speer in hot cor and BTSP configuration, and I used the 154 grain Hornady RN once. Any reasonable bullet out of the 7mm/08 is a cyanide pill for a whitetail.
Either cartridge can be had in a very light rifle. I just recently bought a Kimber Montana in .257 Roberts, and look forward to shooting it soon.
