I have always used this chart to determine levels:
http://www.hoagiesgifted.org/highly_profoundly.htm

Because tests also give varying levels, it's hard to compare one to the other. The SB-V doesn't have extended scoring (as far as I know) but you can use extended scoring on the WISC-IV so you can end up with a much higher score.

Our public school only uses the CoGAT. They agreed to accept our SB-V test only after I supplied them with research that it is a "more valid" test.