It's hard to compare speed feats between the two since both have proven to be extremely fast. People who see Vader lacking in speed are a little bit too attached to the OT, maybe.
I honestly don't know who takes this fight. As far as my understanding of Vaapad goes, it makes you as strong as the enemy you're fighting, so the fact that he defeated Sids doesn't mean too much in this fight. Both are supreme combatants.