1.0 is the "highest", and the only "commercial" round that does that is the mighty .50 cal. As far as your .243 WSSM and the ranges you are shooting, there is little need to be concerned with it. But if you wish to know a little more:

http://www.steyrscout.org/extbal.htm

Little nerdy, but is a good summary.

How much do you wish to spend to start reloading? As Marlin said, you can go from bare-bones to pricey.