Need some Q's answered.(GPU,motherboard,supply)

[nino123]

Im buying some new components to my computer and i need some questions answered.
Im getting:
AMD FX-6300 3,5
Asus M5A78L-M/USB3, VGA, AM3+
Kingston HyperX Blu DDR3, 8 GB 1600 MHz (KHX1600C10D3B1/8G)

Now I curretly have GT 430 2gb DDR3. And a 550W supply.
Do you think its a good idea to replace GPU with something like HD 7770 or gtx 650? Im planning on spending 100-120 € on GPU.
Will my graphic card work in full performance if GPU is PCI 3.0 and mother board is pci x16?
Can i run those specs on 550W supply?
Which GPU do you recomend for gaming?

Thanks in advance!

 

[nino123]

Cant edit: What i meant in 3rd question:
Can i run this graphic card
Gigabyte GTX 650, 1 GB GDDR5, PCI-E 3.0
AMD Radeon HD 7750, 1 GB, PCI-E 3.0
Asus Radeon EAH6670 1GB, PCI-E
on this motherboard
Asus M5A78L-M/USB3, VGA, AM3+
1 x PCIe x16 1 x PCIe x1 2 x PCI

 

[FinneousPJ]

Yes, the HD7770 is brilliant.

Yes, it'll work on your mobo.

Yes 550W is fine.

The HD7770 is my pick.

 

[nino123]

Thanks for the answers mate, any other suggestions on the gpu?