As far as the pressures go, I wouldn't worry about it, As far as things go, the gun isn't really that old, not to mention that the .30-30 isn't what you'd call a high pressure round. Basically, the only problem people really run into with over pressuring old guns is running smokeless rounds in a gun made before smokeless was around, however, in a .30-30, you're safe on that.

The maximum range of any centerfire rifle is mostly dependant on it's accuracy before it's power...I might own a .416Rigby, or .470NE, PLENTY powerful enough to be used on deer, however, if I can't hit anything past 20ft, I'm not going to use them, however, if I've got a .308win that I could hit a deer in the head for every shot at 800yrds, I'd ethically feel confident taking heart shots at that range. I've had .30-30's (Marlin's mind you) that shot under 2" at 200yrds, VERY VERY good accuracy for a leveraction factory rifle....and I would willingly take a shot at a deer at that range with a .30-30. Sights basically only change the accuracy of the gun, so regardless of whether you shoot open sights or a scope, your accuracy should dictate your range.