@Robax91 - Yes, everything is SLI compatible. Not to worried about bottle-necking, because I know I'm going to get some with my system. Question 1, though simplified (excellently I might add), is basically what I'm asking. Question 4 is a great question and wouldn't mind if it got answered. And yes, I do need a new CPU & MB. Thanks for that link, that's a nice website.
As for the RAM, I have 16GB (4 x 4GB), sorry for the confusion. Specs are: DDR3 SDRAM 1333 (PC3 10666), Latency - 9, Timing - 9-9-9-24-2N, Voltage - 1.5V, Unbuffered, Dual Channel Kit.
1. Will the 850w PSU support another 660ti?
2. Does this setup have SLI capability (PSU and MB have SLI compatability)?
3. Is there going to be a bottle-neck (CPU, RAM, HDD)?
4. Will it be worth the cost of another 660ti for the performance gain?
I'm sure a slew of people just want to tell him to get a better CPU/MB combo, but keep in mind what he is asking about rather than posting a pcparticker build without answering his question.
I used this website to calculate your SLI setup and I even put in an overclock to see if it was too much. Your system with SLI will be about 600w, you are good for it as long as that PSU has enough connectors for 2x 660ti SLI.
Another thing to point out is that on older CPUs, the lack of an L3 cache can make an impact on performance, especially for newer games. You should also clarify the RAM specs as well just to see the whole picture (mhz, timing, and how many modules) because 2x4GB would be 8GB, but it says 16GB total. Is that 4x4 sticks or is there something left out.