Hello all fellow Bethesda fans, I am going to respec my computer soon & I'm aiming to be able to run the amazing looking Next Gen Games seamlessly on top graphics. Could someone tell me what the best build upgrading from my specs (below) for under $500 would be?

CPU TYPE:
Intel? Core? i5-2300 CPU @ 2.80GHz
CPU SPEED:
2.82 GHz
SYSTEM MEMORY:
5.98 GB
VIDEO CARD MODEL:
NVIDIA GeForce GT 545 (2 of them)
VIDEO CARD MEMORY:
3.71 GB
VIDEO CARD DRIVER:
nvd3dum.dll
DESKTOP RESOLUTION:
1920x1080
HARD DISK SIZE:
921.75 GB
HARD DISK FREE SPACE:
757.28 GB (82%)
DOWNLOAD SPEED:
2.01 MB/s (16.8 mbps)

(I think their wrong on the download speeds, because the last game I downloaded on Steam downloaded & something like 7 MB/s so...

but I want to know what)

I know that's not all the specs I have & I would supply them, but I don't have the info on hand & I am down the shore for the summer so I don't have access to my desktop... so if there's a specific Mobo or type of ram or what ever, that cant be used with the build for whatever reason, please tell me that so I can replace those parts if they need replacing...

Thanks for the help in advance (and sorry if I'm a little incoherent here, its a late where I am & I've had a LONG day).

I also want to be able to own a Project Shield at some point, so please suggest a build optimized for a NVIDIA 600 series graphics card (I can run 2 cards so if you can tell me what I need to do to run a better card by a different company that would be fine too)