Should I upgrade my GTX 570 or SLI them?

[Inductive Tester]

Right now I have a MSI GTX 570 and is at the minimum or below specs for some games. Should I see if i can get another 570 to SLI or just pony out the dough and upgrade? Will it last me for a few more years or just waiting my time and money? Here is my hardware specs..

i7 3820
16G of ram
Gigabyte X79-UD3
MSI GTX 570
800W Powersupply

Running in 1980x1080 atm enough though higher would be nice but not required. Any information on this would be greatly appreciated. Sorry if i left anything out to help with the question.

 

[Inductive Tester]

Okay ill start looking at some cards. Thank you for your help it is greatly appreciated.