Upgrading ATI Radeon HD 4800 Series

[/b]I recently upgraded my computer and am now looking for a new graphics card to replace my ATI Radeon HD 4870 512mb. My current budget is ~$150.

APPROXIMATE PURCHASE DATE: Within the next couple of months.
BUDGET RANGE: After rebates, ~$150.

USAGE FROM MOST TO LEAST IMPORTANT: Gaming (LoL, SC2, Diablo3, Dota 2, CS:S) in max settings and movies/videos in bluray 1080p.

CURRENT GPU AND POWER SUPPLY: ATI Radeon HD 4870 512MB and a APEVIA 680W Beast Power W/PFC-Black.

OTHER RELEVANT SYSTEM SPECS:
i7 2600K @ 3.40GHz
ASUS P8P67 (REV 3.1) LGA 1155 Intel P67 SATA 6Gb/s USB 3.0 ATX Intel Motherboard
8GB RAM
Windows 7 Ultimate 64bit

PREFERRED WEBSITE(S) FOR PARTS: newegg.com, tigerdirect.com, microcenter.com, frys.com
COUNTRY OF ORIGIN: USA.

PARTS PREFERENCES: No real preference cause I don't know much about graphics cards.

OVERCLOCKING: No.
SLI OR CROSSFIRE: No.

MONITOR RESOLUTION: 1920x1200.

I don't know much about graphics cards at all, so any suggestions would be greatly appreciated. I don't know the difference between Sapphire, XFX, PowerColor, or why I'd need Ti, GTX, GTS, etc. I was looking at AMD Radeon HD 6850/70s and GeForce GTX 550s, but again, I don't know the stats between Nvidia and AMD.

I recommend to you a Radeon HD 6850 or Nvidia GTX 460

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