Help to choose memory

Ideally you want triple channel (or hexa channel) memory for any X58 system, therefore the second set would be a better decision based on that criteria. Depending on your application you might want to look into a lower speed, larger capacity set. After you pass 1600Mhz there are significant diminishing returns in terms of raw performance and you could get a larger capacity 1600Mhz set for the same price.

Considering you have sli gtx 680s Im guessing youre in it for gaming. In that case you could get a 12gb low latency set:

http://www.newegg.com/Product/Product.aspx?Item=N82E168...

This is a good example but you could find other sets (24gb higher latency) for the same price. Hope I helped.

thank you. so the ones you suggest is better than my second link? also you said more capacity will be better choice, what you mean by saying capacity?
also , if I buy 2 sets of triple chanal cards , will it be hexa channel ?

You could buy 2 sets of triple channel yes. Im unsure if they would run the same as a hexa channel kit but as long as the sets were identical it wouldnt cause any issues.

By higher capacity I mean going for 24gb compared to 12gb (6x4gb sticks compared to 6x2gb sticks.) If you primarily do gaming with no major intention of doing video rendering or similar, you'd be better off getting the 12gb set which has tighter timings. This would give you a better game experience (be it noticable or not.) If you do a search on newegg, enable the filter to only show hexa channel kits and you can browse through those sets to suit your needs.

Personally I would recommend the set I linked. 12gb at 1600Mhz with those timings will suit you very well.