When is a good time to upgrade your cpu?

Hi teksyndicate team.
Currently i have a gaming rig that i bought about 18 months ago. Since there are new motherboards on the market that brought me to wonder when to upgrade the cpu and mobo.

Specs:
intel core 3770 (3.5 or 3.4ghz)
Nvidia gtx 780 3gb
pegatron mobo.

Thanks Hax

When it doesn't perform to your desired settings.

What do you do on your computer? If its just games stick with it, I am still running an AMD from 2009 my machine is just fine for gaming.

you have a 3770? You'll be fine for quite some time. Any new CPU (4770) won't be much different performance wise. 

If there is some feature you desperately want in the new chipset then maybe go for it but from a performance standpoint it is is worthless.

if you're out of date by about five generations of product, or the company of your preference makes some truly significant improvements that you 'need'.

When it ceases to do what you need it to do, or when the performance boost that would be gained would be beneficial enough to warrant the money you will have to spend.