There's no single answer to that because the difficulty levels themselves affect the perceived pitch speed:
The pitch speeds in online on the same difficulty (including DD vs CPU) VS. offline are definitely different as well - I know that because I play on Legend offline and can still get blown away by fastballs on Legend in DD vs. CPU play. The devs mentioned this difference in the streams leading up to the game's release.
Anyway...Championship Series is played on HOF difficulty IIRC, which I feel is roughly equivalent to offline Legend pitch speed. But I don't know how that speed would translate to slider adjustments.