Optimization: Crossfire Options vs Single GPU

[Acapella]

Hello everyone! I'm looking to upgrade my system in order to meet next-gen PC gaming requirements. My currents specs are as follows:

Processor: i5 4670k overclocked to 4.3ghz
Graphics: Radeon 7870 ghz edition
RAM: HyperX 2 x 4 GB 1600 mhz
Power Source: Corsair CX500M 500w
Motherboard: Gigabyte GA-Z87X-UD4H
Display: 32" Seiki 720p TV or AOC 16" 16:9 and 17" 5:4 (forget brand)
Hard Drive: Seagate Barracuda 320gb
SSD: 128 GB Crucial M500

I don't really have a budget($500 available), but that being said, I'd prefer to stay on the cheap side, while not sacrificing too much in the running of next-gen games. The options I'm currently looking at, while I'm open to any other suggestions the community has are as follows:

1. A friend has an extra, albeit used Radeon HD 7970 that he is offering for $100. I could take that solo if it'd be enough for next-gen, but I don't know if it is. I could also crossfire it with a 280x or another 7970/7950.

2. Upgrade to a Radeon R9 280x or GTX 770.

3. Crossfire my Radeon HD 7870 with a R9 270x or another 7870.

I also may consider a different display option, hopefully a monitor larger than 16" that supports 1080. I don't know how much my 720p TV lowers overall visual output, but if someone would like to explain I'd love to know prior to deciding whether to make a change there.

I think any two card system would require an upgrade in power source to at least 600W, maybe more. I have no clue which of my options will provide the best performance, and whether additional performance will be worth the additional cash. I'm currently a senior in high school who has some extra cash left after a summer job, but is currently unemployed. I spend less than three hours daily gaming, but I like to stay up to date on hardware when able. Any suggestions are welcomed and any expertise is greatly appreciated. I thank in advance all who will decide to give time to helping me make a decision.

 

[Somber]

Running one GPU is better than 2. Some games dont have optimization for 2 GPU's so in order to play them youll have to disable one card. I would go with a single gtx 770

 

[prit87]

a single strong card is always better than two mid range gpu crossfire or sli comes with lots of drawbacks...
more power consumption
more noise
micro shutters
not all games support sli or CF in that case u have to manually adjust them..
so go with a r9 280x or gtx 770 whatever u preffer they will give u good enough performence at 1080p resolution at ultra settings but still u have to upgrade your psu they both require around 600 watt psu r9 280x needs 30amp on a single 12+ volt rail where as the gtx 770 needs a 42 amp @ 12+ volt.......so get a good 600 - 650 watt psu from seasonic or xfx ...

 

[Acapella]

How does the 7970 compare to the 280x and gtx 770? I've checked out gpuboss, which is generally really helpful, but the results for the comparisons are not in agreement with other studies and experiences in these specific cards. Basically, would the 770 or 280x outshine the 7970 considerably?

 

[prit87]

How does the 7970 compare to the 280x and gtx 770? I've checked out gpuboss, which is generally really helpful, but the results for the comparisons are not in agreement with other studies and experiences in these specific cards. Basically, would the 770 or 280x outshine the 7970 considerably?

r9 280x is a re branded version of hd 7970 so they are almost same with the r9 280x being newer and a bit tweaked...and gtx 770 is more or less similar to the r9 280x in performance..