Hd 6850,hd 6790,hd 7770 which one is the best for gaming?

Depending in what you are going to play... I suggest for 1080 the HD6850, its still a good card and you can find good deals online.

The HD 7770 uses less power and runs cooler and have great overclocking potential, but at high resolution the 128bit bus suffers. Thats why the HD6850 and its 256bit bus will give you and advantage at high resolution, also it will run better on DX 9 games and it drivers supports its more mature.

For the PSU, getting a well-branded 500W will be plenty for your needs, and well suited for a CPU+mobo upgrade in a future.

I like Corsair, Antec and seassonic. Some Cooler Master GX series are good but you really will want to spend your money in a realiable brand.


http://www.newegg.com/Product/Product.aspx?Item=N82E168...
HD6850

And

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

There are good deals, also maybe you can get the HD7770 a little cheaper, and cut down the PSU for something with less wattage and cheaper, but this are just general recomendations, its all up to you pal  

All three cards are somewhat comparable.
The 6850 might be a touch stronger.

Your 450w psu should be sufficient for the 6850 or 7770 if it has one pci-e 6 pin connector.
It will probably not work with a 6970 that needs 2 such connectors.

What card are you currently using?
When you upgrade, make it a significant jump, or you may be disappointed.

The newer 28nm based cards(GTX6xx and 7xxx) are more power efficient.

but buddy,the thing that concerns me most regarding the psu upgrade is that my hard disk drive supports only pata cables but recent psu's come with sata cables so will i be able to run the pata powered hdd with sata power cables?

No, you can't use the sata power leads, but all psu's will come with 4 pin molex connectors. They can support splitters or be daisy chained if need be.
A hard drive does not use significant power.

where do i get this molex thing?and are u sure that the molex connectors can connect my pata cabled hard drives?

This is what a molex power connector looks like:
http://en.wikipedia.org/wiki/Molex

I would be very surprised if your psu does not have a few.

Best answer selected by krishnakhatri.