I would wait. In fact that is what I am doing since I am still using a Q9450 @ 3.0GHz.
I guess it depends on what you do with your PC. Haswell is expected some time in Q2 2013 so that can be anywhere from just over 3 month from now to just over 6 months from now. No concrete answer as to how much better performance will be over Ivy Bridge. I think it will range between 6% - 10%, but betting on about an 8% increase in performance assuming same clockspeeds. I believe Intel is focusing more on reducing power consumption than increasing performance.
I believe Intel will focus on performance in 2014 when they release Broadwell.