for a single 6950 1gb is it necessary to get a k series i5 processor ..i know that overclocking will give performance increase upto 40% but is it necessary ..instead of buying a z68 mobo can we get a h67 mobo and a 20gb ssd for os with a non k processor
Overclocking is never necessary. It is simply done to get more power from whatever we already have or for fun.
The i5 CPU is very good and powerful it can coupled with a 6950 with no bottleneck IMO.
Also you can overclock with a P67 mobo no need for a z68