Is this PC bottlenecked? and what should i upgrade to?

hi i am a gamer with a above average PC however whenever i paly games such as CSGO there is a chance that my whole PC will just freeze and i can hear an audio loop. I think this is my graphics cards due to that i have had alot of issues with them where they have crashed. i was thinking of updating to a GTX 900 series probably the 960.

so what is the problem?
is my PC bottlenecked?
what should i upgrade and what to?

Specs:
OS: Windows 8.1
CPU: interk Core i7 3970x CPU @ 3.hGHz
RAM: 32 GB
Mobo:Asrock Extreme 11

Which GPU do you have now, I wouldn't think that your processor is the problem ?

Yea, if no dedicated graphics card now you need to get one.

sorry i just forgot to include them i have 2 gtx 660ti in sli

Is your PSU powerful enough?

EDIT: Have a look here: Build an SLI PC - Certified SLI-Ready Power Supplies | NVIDIA

i have an EVGA 1000watt and i was thinking of upgrading the GPU

That is definitely a capable PSU. Sounds like you are pretty set on updating GPU and looking for support. Go for it if that is what you want to do. Even if the problem is still there you will have one of the latest GPUs and can go from there fixing the other problem.

Make sure you have the latest drivers for you motherboard, sound, etc.

what GPU tohugh? my budget is around £200

Now that is a very subjective question. There are so many choices it is hard to recommend one particular card. Some people prefer AMD some people Nvidia. I would just try to get the biggest bang for the buck and run comparisons on those in the same price range.

Just a quick search and I found this one in your price range with good reviews: GTX 960: ZOTAC - It's time to play!

Your computer should not be freezing so I would not spend any money on new graphics until you sort that problem out first. And not sure what you mean by audio "loop" but if that might be described as "stuttering", you could be having DPC Latency issues. See DPC Latency Checker.

Have you scanned for malware?

What are your temps? Is the case interior clean of heat trapping dust?

While your PSU should be more than capable, even the most respectable brands can make faulty ones. If your system is clean of malware and dust, does not have latency issues, then I would swap in a known good PSU just to ensure you are supplying the rest of your components good, clean stable power.