Right now I am flying from EGLL to KSFO at 30000 feet yet when I look at the FS9 altitude it tells me I am at 29589 (When I press Shift+Z). My speed is also different 324 on the 744 and 303 on FS9. I am inclined to trust the 744. Just wondering. Any insights as to this discrepancy?

The altitude discrepancy comes from the pressure being different from the 29.92 mmHg/1013 HPA (using standard pressure is just a convention and not coming from the pressure actually being fixed)./ Jesper