Help with GPU

[Oxygene_]

Hey there guys , I have had a (very) low budget gaming pc for a while now that I built myself and I think it is time for an upgrade , the main thing that is slowing down my game performance is probably my GPU , it is a AMD Radeon HD 6450 (Very low budget , I know) I was hoping on getting something like a MSI AMD R7770 or along the lines of that. My biggest concern is will it work with my pre-existing components? I wont put everything down (Such as the optical drive and similar add-ons) but if they are necessary , I shall

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Specs
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PSU: CiT 500W 12cm Silent Fan Dual Rail Power Supply - Black Edition
Motherboard: MSI 760GM P21
GPU: AMD Radeon HD 6450
RAM: 8GB Corsair DDR3 1600
CPU: AMD Athlon III X2 270 running at 3.4 GHz


Thanks for reading , any help or suggestions are appreciated!
Anything else you need , I am willing to give! Thanks again!

 

[Jared Jensen]

What is your budget? Because there are many great GPUs for their price so depending on your price, we can see which one is best for you.

 

[Oxygene_]

What is your budget? Because there are many great GPUs for their price so depending on your price, we can see which one is best for you.

I have £100 right now but will be getting a lot more for Christmas , so I will have £350-£400 to spread across the upgrade , that's why I was thinking something like the 7770 , seems to be very good for the price , but any suggestions are greatly appreciated