Gtx 980 vs titan x vs titan z?

[Medically]

Which one would provide me with the best quality? I cant afford the z but would getting the x over the 980 be worth it? And i keep hearing about 980 ti and 980 sli. Is there a different between those and regular 980? Thanks

 

[KeelinTy]

Two 980s In SLI will be the same power as a single Titan X. A single 980TI is almost as powerful as the Titan X. Just with 6gb of VRAM instead of 12gb

 

[17seconds]

Anything with a Titan in the name should never be a purchase consideration, unless you are one of the very few people who actually need a bunch of VRAM. The reason is that custom, factory overclocked GTX 980 Ti's are faster cards for about $350 less. A GTX 980 is at a different level beneath the 980 Ti. Get what you can afford, so long as it has the numbers 980 in the name, and not Titan.

http://www.techpowerup.com/reviews/Zotac/GeForce_GTX_980_Ti_Amp_Edition/30.html