iMacs (and most other stuff) usually gets updated after Back-To-School is over.
At least, historically. Haven't taken much notice recently (not in the market anyway and certainly not in school anymore...)
But yes (checking), the last three updates were November, September, October.
If you can do with your 2011 model for another six months, I'd do that and then decide if you want to pick-up a 2014 model at a clearing sale/refurb or go for the new one (with unknown bugs...).
We're not talking about some historic Apple 1 that represents a once-in-a-lifetime investment opportunity - these things get made by the thousands each day and there's absolutely no need to rush IMHO.
Unless there's a business-need, of course.