what problem ? btw which one gtx760 or sli gtx660 good for rendering ? i'm not a gamer but i also play games like bf4 n so on.. but i focus more on rendering, 3d modeling, photoshop, etc.
my pc build :
cpu : intel xeon 1270 v3
memory : Gskill RipjawsX Blue 1866 DDR3 RAM 16GB ( clearing stock last month )
intel ssd 160gb..
AFAIK most pro application can't take advantage from SLI. so you need to check back with the software that you were using. some software can take advantage from multiple gpu like OTOY Octane although it is not because of SLI but because of more CUDA cores available on the system. in general taking a single 760 might be more logical choice for you since your priority is not gaming
If I'm not mistaken, 3D modelling/rendering, photoshop, are CPU-intensive tasks. Video editing software is what takes advantage of the videocard the most, especially if you are using the latest version of After Effects since Adobe have optimized their (video editing) software for Nvidia.