Single is better than sli imo. On what settings would you like to play that game?
I used to play MW2 on Intel HD 2000, few time when enemy near and attacks, the real time rendering fails and delay occurs.
In BF3, Intel HD 2000 is totally fail to response in realtime, So I must have to buy a faster GPU.
I want real time response in gaming. Medium/low graphics settings are acceptable.