what games are you playing right know Call Of Duty and what games are planning to play in the future maybe BF5?.
If that GTX 660 is good know find something similar new or the same card second hand other option would be to get a GTX 1050TI that would be the equivalent card to date to match or perform slightly better than that GTX 660 this would be my answer if you play games like Call Of Duty2 MW2 FT1 World at War all hosted by XI.
For a game like BF5 at the moment probably a 1060 or a 1070 and you be good to play that with 80 frames or so on limited settings and yes a game like that on low looks way better then all the call of duty,s on ultra high.
your system
I7 -3770 processor,
16 gb DDR3 memory,
2 TB hard drive,
256 SSD.
GTX 1060 or 1070
this will probably last you 2 gaming years playing the newer games that come out but on low settings for the older games with a GTX 1050TI this machine is pretty much future proof.
Gr Dessy hope the info helps happy gaming.