To get the perfect BDC turrent you should shoot your load at 50 to 100yd increments to 1000 yds, record your data on the sheet from Kenton and pay a few more bucks and have it done by Kenton.
Leupold is cheaper, and using the velocity and BC of the bullet your shooting, will get you a turrent that is pretty darn close, but at 600 to 1000yds the BDC might be off a click or two. Plus, myself and one of my buddies have recieved custom turrents from leupold that were screwed up. I don't know who is running the lazer engraving machine at leupold, but I think they are being paid minimum wage.
Then you have the Redneck option. Buy some heavy duty medical tape at Wal-Mart and a couple fine point sharpies in different colors. Shoot your rig at all distances and make your own BDC turrent with the tape. Shoot your rig in this configuration to make sure thats what you want before dropping the $$$ to have it engraved. I just finished six days of rainy deer hunting in Mo using the aforementioned Redneck custom turrent and it held up perfectly.
Smacked a big 12pointer with 7mm Rem mag, 180 Berger @3000fps at 1500yds. OOOOPS! Sorry, it was more like 150yds. But hey, I was ready for a long shot!