I am aware that we don't use SSJ multipliers for speed but I just thought I'd say that SSJ3 should be 400c using those and Vegito is far above them (I've seen a 400x multiplier thrown around but I don't know where that came from). So MFTL does seem fairly justified, but it should probably have a note next to is that this is implied by both the massive boosts in power since Namek and the SSJ multipliers.
EDIT: Potaro is said to be a multiplier of both fighter's strength. In that case...
Vegeta - 250,000
Goku - 3,000,000
3,000,000*250,000 = 750,000,000,000
SSJ3 can be calculated to have a PL of 1,200,000,000 through the SSJ multipliers (which do multiply PL linearly).
750,000,000,000/1,200,000,000 = 625x multiplier, while again we aren't sure it's exact relation to speed it does definitely back up at least MFTL