Need advice on what graphics card to get.

Hi so i have been looking all over for the right card for me but its really hard to decide + I really dont know what will and wont work. I copied the *How to Ask for Advice about Choosing a New GPU* template to hopefully make things more simple.

APPROXIMATE PURCHASE DATE: As soon as possible(few days) BUDGET RANGE: CDN $300-500 Before / After Rebates

USAGE FROM MOST TO LEAST IMPORTANT: All i really want this card for is Gaming(Skyrim, GTA4, l4d2, mass effect 2/3, many more)

CURRENT GPU AND POWER SUPPLY: GeForce gtx 285 and DELTA ELECTRONICS GPS-750AB-A 750W

OTHER RELEVANT SYSTEM SPECS: Not sure exactly what to put here so some help would be nice. Heres my best shot:
Operating system:Windows vista home premium(6.0, Build 6002)
System manufacturer: Gateway
System Model: FX6801
Processor :Intel core i7 CPU 920 @ 2.67GHz
Memory:12278MB RAM
Directx11. ^SORRY if too little/too much info^.

PREFERRED WEBSITE(S) FOR PARTS: Really not sure. Heard good things about newegg but never tried.

PARTS PREFERENCES: Well the only graphics card i have had was the nvidia geforce gtx 285 so i cant compare anything to it. Although im SLIGHTLY leaning towards nvidia.

OVERCLOCKING: No idea how to overclock. Looked into it a long time ago and was too confusing   So maybe a OC'd card already that i wont have to mess around with? I'm not sure.

MONITOR RESOLUTION: 1920x1080

ADDITIONAL COMMENTS: Well right now my card gets pretty heated so maybe a better then stock cooling? I am thinking of adding some fans to cool down my pc in general. Warranty would be extremely nice. Must have atleast 1.5gb of VRAM. Must be fairly simple to use/setup/configure. OH i almost forgot. I have a samsung S23A750D monitor with Display port. Right now its hooked up to a dual link dvi to mini dp converter to work on my gtx 285. I was hoping for a pure DP connection. No converters.
Thanks SOOO much for any help.

Maybe a little info on the HD 7870 or the HD 7850. Some1 suggested them and they look good but was a bit concerned how well it would work and how well it would work with my system.

Sapphire Radeon HD 7870 GHZ OC 2 GB DDR5 HDMI/DVI-I/Dual Mini DP PCI-Express Graphics Card 11199-03-20G
http://www.amazon.com/Sapphire-Radeon-PCI-Express-Graph...