According to http://www.airwar.ru/enc/bww2/me310.html, the Me 310 and 410 were designed in parallel, and were mostly identical. The difference was that the 310 was optimized for higher altitudes; therefore it had longer wingspan, pressurized cockpit, and no automatic slats. Two versions were proposed: Me 310A-1 as a Schnellbomber (high-speed bomber), and Me 310A-2 as Zerstörer (destroyer). The only prototype, registered VH+AQ, was converted from a production Me 210A-1 #179; it made its first flight in September 1943. The 310's wingspan is a question: in the text it's claimed that it was 0.65 m longer than at the 210, but the technical data specify 17.90 m wingspan which is 1.55 m longer in comparison to the 210.
William Green in Warplanes of the Third Reich, gives the same dimensions, 17.90 mts for the Me 310A-1, against 16.35 mts for the Me 210A-1. With the wing area being given as 37.70 sq mts for the Me 310A-1 and 36.20 sq mts for the Me 210A-1.