If you are doing CF, then you must be experiencing micro-stuttering, which will significantly vary FPS (sum of inc.) results. As such I wouldn't worry about your setup being 75% that of internet benchmarks.
As for upgrading, unless you are dead certain that you've hit a CPU bottleneck limiting your GPU potentials, and affecting gameplay significantly, I wouldn't buy the 2500k. Remember, there's not much difference between the two in terms of CPU horsepower, and CF configuration means you'll be mostly bothered about the disadvantages of it.