Choosing the right graphics card for my next PC (Advice wanted)

I am getting ready to build a new PC and since I do gaming and make YouTube videos, making sure I have a graphics card is important. It can also be one of the more tricky choices for me because my vision is not the strongest and I tend to use lower resolutions then what the most modern / current stuff is set up for. (Right now I'm running at 1366 x 768 and I honestly don't see that changing.)

My PC will be used for:

-- Scrivener / Microsoft Office
-- Photoshop Elements
-- Windows Movie Maker
-- MMOs (World of Warcraft, LOTRO, Final Fantasy XIV, etc.)
-- Skype
-- iTunes
-- Google Chrome

Here are the processor and motherboard I'm looking at getting:

AMD X6 FX-6300 (95W) Six-Core Socket AM3+, 3.5GHz CPU, 8Mb Cache, 32nm (FD6300WMHKBOX)

http://www.canadacomputers.com/product_info.php?cPath=4_64&item_id=053298

ASUS M5A97 R2.0 Socket AM3+ AMD 970/SB950 Chipset
- Dual Channel DDR3 2133(O.C.) MHz, 2x PCI-Express x16
- GLAN, 6x SATA 6.0Gb/s, 2x USB 3.0, 6x USB 2.0
- ATX

http://www.canadacomputers.com/product_info.php?cPath=26_335&item_id=051996

A few more quick facts:

1. I will be sticking with one graphics card. I have no interest in Crossfire or SLI.

2. I don't intend to do any type of overclocking.

(In short: I'm a bit of a paradox: I like choosing the parts for my PCs, but I don't tend to fiddle with them when I buy them. This is in large part due to my own vision and due to my brother's history of breaking things when he tries to 'improve' them. I say: buy something that will work right outta the box. *Please note that I am strictly speaking for my own needs with regard to that last statement. I have a great deal of respect for those who are able and willing to advance the quality and performance of their equipment through knowledge and study--I just don't think it's my thing, and I don't have the funds to risk it.)

Here are the cards I'm looking at:

Sapphire (11200-07-20G) Radeon HD 7850 2GB GDDR5
- 860 MHz Clock, 4800 MHz Memory
- PCI-Express 3.0, Dual-Link DVI, Dual Mini DisplayPort, HDMI

http://www.canadacomputers.com/product_info.php?cPath=43_1200_557_558&item_id=053225

Sapphire (11199-19-20G) Radeon HD 7870 OC 2GB GDDR5
- 1050 MHz Clock, 4800 MHz Memory
- PCI-Express 3.0, Dual-Link DVI-I, Single-Link DVI-D, DisplayPort, HDMI

http://www.canadacomputers.com/product_info.php?cPath=43_1200_557_558&item_id=058063

EVGA (02G-P4-2662-KR) GeForce GTX 660 Superclocked 2GB GDDR5
- 1046 MHz Clock, 6008 MHz Memory
- PCI Express 3.0 x16, DVI-I, DVI-D, Display Port, HDMI

http://www.canadacomputers.com/product_info.php?cPath=43_1200_557_559&item_id=052927

***

I have an ATI Radeon HD 5850 in my current build and have been quite happy with it.

For what I'm doing and how I set my stuff up which of these cards seem like the best match for my needs? If you have any particular reasons for one card over another, I'd love to know Why. I like making informed decisions whenever possible.

Thanks and have a great day!