Ranging error can introduce the largest problem, wind the next largest, and if you get a good range on the target it can be the largest as you have probably figured. Getting solid velocity readings at a few temperatures ranges you'll hunt in will give you the correct velocity to work with each time, very important and any ballistic program will show you just how much. Atmospheric temp and pressure will change the effective BC and most ballistic programs will show these effects on bullet drop and wind deflection too. You're in search of a MV ES (extreme spread) that is low or groups will get more and more vertical on you the farther you shoot. A higher BC bullet will give you less wind drift at LR, although it may not shoot as flat in the intermediate range, it will however likely have higher energy most all of the way out. Dialing in a few extra clicks for any extra drop is the easy part, at some point they will drop less than the faster lighter bullet with its lower BC. A good rangefinder and wind meter, Sherpa, Kestrel, will serve you well if you don't already have them. Making your drop charts from actual fired range data is a must, here's where you'll build your wind doping skills too. 4'x8' sheets of plywood work great for catching blown off target bullets... you'll learn ballistic programs do real well with wind speeds and is really necessity to either have charts with you with varying speeds or a handheld Palm Pilot with a ballistic program in it to give you the exact data and corrections.
Take a good load and practice, practice, practice. Of course there's even more to consider but those are some main things and a start. There's lots of great reading here too, the search function here can help you find alot of specific info you might be looking for too.
Books:
Precision Shooting at 1000 yards
50 Caliber Sniper course
Precicion Shooting Reloading Guide
and much more on the web too.
Good luck, you'll be at 800 yards in no time.
