Here's my experience for the approximate difference in performance.
You are talking about a 200 MHz difference on a machine already running at 2700 MHz.
That is a minor bump relatively speaking.
200 MHz is very noticeable if you are talking the difference between a system running at only 4 or 5 MHz and one running at 200 MHz.
But when you're already at 2700 MHz, I'd say save your money and spend it on something else (like memory).
For a rough comparison, though on an older design, I'll tell you about my recent upgrade.
The Mac Pro in my signature used to be a quad-core 2.66 GHz machine. I upgraded it to an 8-core 3.0 GHz machine.
That's essentially increasing its speed by 340 MHz and adding 4 more processors.
In my minor tasks, the difference isn't really noticeable.
But, then again, I also do a lot of tasks that will fully max out all cores 100%.
So, with my use case, a task that would use 100% of my 4 processors and previously took 90 minutes to complete, now maximizes all 8 of my processor cores, and takes 25 to 30 minutes to complete.
But that is with not only increasing the speed by 340 MHz, but also doubling the number of processor cores working at that higher speed.
So on the system you're talking about.... For small tasks, you won't see any difference. And if you push your machine hard like mine, perhaps expect to shave 5 minutes off of an hour task (because you're not increasing the number of processors, just the speed).
