Yeah, most game engines like Portal's uses absolute speed relative to the coordinate system (which doesn't change when the coordinate values change), in addition Portal technically doesn't actually implement "wormhole type" portals and instead superimpose a clone of the polygons near both portals behind the other (to preserve expected object collision behavior around the portal) plus doing tricks with virtual cameras, so if you fixed the bugs with moving portals then it would be A.

But if you implemented proper relativistic physics with proper wormhole type portals you'd get B.