This may not help you but here I go.

You can make an new PC for around 300$ to 400$ and play the games of the now with good high end GFX well not the best but can probably games of the now at full and you can save if you use your harddrive.

Note: Also note APU is a GFX and CPU all in one

Case: http://www.newegg.com/Product/Product.aspx?Item=N82E16811147099 $49.99

MotherBoard: http://www.newegg.com/Product/Product.aspx?Item=N82E16813131796 $64.99


Best APU: 4 Core APU http://www.newegg.com/Product/Product.aspx?Item=N82E16819106001 $104.99


PSU Comes with case


GFX card: Part of the CPU/APU but I will say it's on par with a mid 6000 HD series.

Ram If you have DDR3 use yours if not take your pick here i can find cheapest just to get it to run ay $9.99 but for this example I'll use a $51.99 Gskill RAM Link to take your pick: http://www.newegg.com/Product/ProductList.aspx?Submit=ENE&N=100007611+600006050&QksAutoSuggestion=&ShowDeactivatedMark=False&Configurator=&IsNodeId=1&Subcategory=147&description=&hisInDesc=&Ntk=&CFG=&SpeTabStoreType=&AdvancedSearch=1&srchInDesc=


HDD take your pick of any SATA HDD recommended you pick 7200RPMs Drive the higher RPM ones holdless and I call them suicide harddrives due to there fail rates or use the one you have provided if it's SATA in fact here is a link too all SATA 3.0 HDD with 7200RPM http://www.newegg.com/Product/ProductList.aspx?Submit=ENE&N=100007603+600003459+600003340&QksAutoSuggestion=&ShowDeactivatedMark=False&Configurator=&IsNodeId=1&Subcategory=14&description=&hisInDesc=&Ntk=&CFG=&SpeTabStoreType=&AdvancedSearch=1&srchInDesc= But I'm picking the one I like and that one cost 79.99 1.5 TB Seagate

All that comes too $351.95 without tax.

Note: I also used power supply Calculator to make sure it was good I used 3 2700RPM and about 4 8gb ram in the calculator and got 315W so I used 400W PSU but you can use yours if you think it will work and hell may be better.

Another note APU will be like a mid tir 6000 AMD Card

Now for the question at hand

Best will only be the best till 6 months and to be honest it's not worth getting the best GFX card AMD 6000 cards are good, cheep and will play anything of the now and prospectively 5 to 6 years from now too and I'm not to keen on  nividia cards but I would say there better at making games or videos (things that would require rendering) and I'm sure there 1000$ card could beat AMD cards any day when it comes to the best.

If all you want to do is play newer games at good Frame rates go with any card made last year so it will be cheaper (I know nividia had some GFX card issues on them in the past like over heating and ect. so that's why not too keen on them since I stopped looking at them since they cost an arm and a leg and that issue turned me off a long time ago.) But now a days there looking good once more and Some times I wish I had one since I do video rendering.

So I hope I was able to help at all but you seem set on what you want to be fair use your brain on this it's not that hard to compare and contrast what is better.
 

honestly it probably doesn't make a difference. i've had cards from both and never had any problems with either.

On that note I too have the same processors. But I never had any issues with an AMD video cards but to be fair 7970 is going to be better and faster if you get the right one. but if you do some video editing or 3D rendering then go with the GTX 670.

why would this be spam

I went ahead with the GTX 670 because I snagged it for a low 349.99 on Newegg as part of a holiday deal.

On another note, I have the ever-so CPU-intensive Guild Wars 2 and would like to avoid framerate dips. After I stick my new GPU in, would my Phenom II X6 3.2 ghz hexacore CPU be bottlenecking the GPU? I was considering an upgrade but wasn't sure if it was really worth it.

if you mean your going to get an 8 cores just make sure you don't get a Bulldozer  Faildozer. To be honest nvidia card's have cuda cores that aid processing like a CPU (hence better for rendering stuff but since the games you play are hard on CPU this should help.). So I would hope not one way to find out install it and see for your self.

your computer seems to be pretty good. idk y you'd upgrade right now. If you've got money burning a hole in your pocket, then maybe wait until Intel puts out their Haswell chips, it's gonna be another architecture change and with some new bells and whistles and be a lot more efficient because of the die-shrink.(14nm fab i think)

idk I'm still running a q6600 with an 8800gts and other than throwing an SSD in it, I think it's been more than capable of running whatever I've needed to. Sometimes I get the itch to go for an upgrade but i really can't justify it for maybe playing half dozen pirated games or w/e. I'm probably gonna break down and get an iMac when I NEED a new computer.

I upgraded from that 8800 GTS to a HD 5770 and that was wonderful bang for buck. Plays all current gen games. Where I fell short was getting a 555 BE processor (AMD) instead of the 550 where you can unlock the 2 hidden cores for £60. I'm hoping when GTAV eventually meanders its way onto the PC it will be better optimised.

I went ahead with the GTX 670 because I snagged it for a low 349.99 on Newegg as part of a holiday deal.

 
The 670 is a good choice. Tom's Hardware included it in the System Builder - $1000 PC in December and in the Best Video Card for the Money here in January.