Our daughter took the WIPSI at barely age 4..then the Stanford Binet 4th edition a few weeks later. 8 points higher on SB. Then again at age 6 and 8yrs...only on SB 5 leveling out at 16 points higher than that first test.
They are not the same and the SB does not penalize for processing speed.
Maturity can matter. The type of test/strengths of child can influence a score.