Help me choose a GPU

[RLSSpeedy]

So i have recently built a PC and I am trying to decide on a graphics card to go with what i have put together. I'm holding my breath for winning the 290 toxic comp but, failing that I'll need to come up with an alternative, and I'm hoping the switched on cookies on this forum can lend me a hand.

Heres my build so far:
CPU Corei5 4670k
Mobo Z87 GD65 MSI Gaming
RAM 8GB Corsair Vengance
PSU Corsair RM650
SSD Samsung Evo
HDD Two Shitty 350Gb hdd in Raid 0
Case Corsair 330r

Playing: Starcraft2, Titan Fall, Batman Arkham Origins...

ive been looking at the R9 270x, fits nicely at around £150 ($250) which is about top end of what i'd like to spend.

So my questions are this:

* AMD seem to have two product "trees" the R9 2xx and the "7 thousands-and-somethings" what's the difference? is it just a rebranding exercise or is there actually any real difference?

* Clock Speed versus on board Ram - I've seen a few boards with the same R9 270 designation, some with 4GB GDDR5 and some with 2GB GDDR5, and then differences on the clock speed. How does this affect its performance?

*AMD vs Nvidia....? Pros Cons of both...

*is there a better manufacturer...?

With everything else i think I've been able to way up the performance and the compromises for all the items i have brought, but I'm finding it very difficult for the GPU...

Thanks for reading.

Rich

 

[jacknamvar]

nvidia gpus have physx and make some real pics in games but i think amd is cheaper (maybe) .