I use passmark.com to determine where a CPU is at in general performance.
Just click benchmarks at the top. Then click the searchable list.
Your current cpu scores roughly 2698 on average.
An 3570K scores about 7151 on average.
An 3770K scores about 9623 on average.
A hard number is ok just to give you a ballpark idea.
Intel's prices don't change much...
Only perhaps a marginal price drop after Haswell is out.
There will always be something new around the corner.
Upgrade when you feel your system is not up to par.