Devs stated on many occasions that multi core support needs complete rewriting of the game engine and therefore wont happen for Rebellion.
Even now game doesn't support 2 cores. 2nd core is used for loading game only. It is not used for anything else.
What you can do is OC your CPU if possible. I have 2 machines. One 4MHz other 2.7MHz. On first one game runs much smoother for longer and even Distant Stars with 10 players with 4000 fleet supply each is playable while on other it turns into screenshots.
They didn't mention SLI but I don't believe it will happen either.