Few queries on build

[swordsy]

Hello all,
I just have a few quick questions about upgrading my system

I currently have.
Fx6100 running aftermarket coolermaster heat sink
(Mild overclock)
8gb corsair vengeance low profile 1600
(Corsair - CML8GX3M2A1600C9)
El cheapo ASUS M5A78L-M-LX-V2
Gtx 260 gigabyte OC black edition
500W cooler master psu (3 years old)
4× assorted 500gig and 1 Tb drives
Running win 7 64 ultimate.

(Re)Built the system last week to include the mobo and the fx6100 and decided that I'd like to take it up a level.
So I'm looking at:
ASUS - M5A97-EVO-R2
Fixing my mistake of going too cheap with the other board
ASUS - HD7870-DC2-2GD5-V2
Another 4 gig of ram (Corsair - CML8GX3M2A1600C9)
Seagate 3tb sIII drive
Seagate 1tb SIII drive (for OSes and game installs)

I mainly use it to run games ranging from skyrim/dishonored
Star trek online. Planet side 2. Dayz. Usually running video /youtube on a second monitor.
And very occasionally rendering 3d images
My questions are basically.

Should I bin the psu and go for something closer to a 750W?
Is the extra 4 gig of ram worth it.
Should I bite the bullet and go for a hd7950 or possibly can I go something lower? (Ati is a must, linux and nvidia don't agree)
Or Should I just xfire two hd7770's?

And does anything stand out as silly and irrelevant?

Thanks.

 

[swordsy]

Sorry about the format of this.
It was written on my phone in a motel room