I have G7 BC's for Bergers and some other brands as well that are based on test data and are accurate within +/- 1%. If you have a particular Berger bullet in mind, I can provide you with the G7 BC. If it's a non-Berger bullet, I might
have data for it.
Lou is correct about flat based bullets being a better match to G1, so if you're looking at flat based bullets don't worry about G7.
Most long range bullets with boat-tails (secant or tangent ogives) match G7 better than G1.
Lou is also right about conventional ballistics programs not accounting for all of the subtleties of a spinning bullets flight. However, if your bullet has adequate stability you can predict a very accurate trajectory out to 1000 yards by entering accurate inputs into the program. Most programs won't account for spin drift, coreolis acceleration, or other effects that are 'second order'. You'll get a very good trajectory from a conventional program that will probably be within the accuracy of your equipment.
Considering the second order effects can help to improve your chances of a first shot hit, but as Lou stated, the inputs required and the cost of a program that's capable of doing the math is prohibative.
Here's a link to a couple articles that talk about some of the effects not considered by typical ballistics programs, and the affect they can have on your max effective range:
Homepage of Bryan Litz - A Bravenet.com Hosted Site
Click on 'Max Effective Range' on the left.