The HD6850 and GTX 460 are basically equal in performance at reference speeds. At the prices you linked I would only bother with the GTX 460 if you plan on giving it a high overclock.
i will not overclock i am talking about the performance at stock clocks
and how is 6790 good enough it will save my money
comparing 6790 to gtx460 abd 6850
all in power requirements and in performance
and suggest me psu that can support all these above cards
these are available now i am looking a psu from 5000rs to 6000rs or may be 500rs more