It is tough to measure. They need a new leverage situation of 'wicked high leverage', unfortunately it would be a small sample size. Look at playoff stats compared to regular season. Ortiz ops is higher in playoffs, not by much, but most players go down due to better pitching. I looked at a few players who have a fair amount of post-season at bats, Ortiz and Jeter went up, Chipper Jones, Manny Ramirez, A-Rod, Mickey Mantle all went down. By people who believe in clutch, Ortiz and Jeter are usually prime examples. I don't personally feel this is about upping your game, but not feeling the pressure when everyone else does.