The term "RG" is used generically only to describe cable sizes based on the original copper braid/solid polyethylene dielectric construction. Therefore there are many RG-6 type cables however those constructed with a foam polyethylene dielectric and an 18ga center conductor will all exhibit the same attenuation characteristics. This is the case with cable swept to 1000Mhz or to 2500Mhz. That's not to say that one tested to 1000Mhz will not perform the same as one tested to 2500Mhz. There is no difference in the cables, only that perhaps the 2500Mhz one is selected from the "cream of the crop" and you can be sure of what you are getting.
-Hal
