1. CPUs help a lot in smoothness, experience, and remove stuttering/lag/jerkiness, even if FPS aren't very different, the experience can be a lot different and improved. Unlike GPUs where FPS and MS are the only criteria, for CPUs it isn't the same. There is no research for this except my experience but it holds true if you have the aptitude and observational power to comprehend it, which 99.9% people can not understand but can feel the difference in a blind test.
2. In Starcraft, your new CPU in FPS terms is about 100% faster which is unlikely over a single CPU generation.
3. 2500k and 3570k are essentially the same performance. So you are unnecessarily adding a generation which added 0 value to anything at all.
4. The newer CPUs overclock higher as well, which you didn't take into account.
5. Try playing with a fast card on a Q9650 at stock, then at 4GHz, then with a Core i3 and then with a Core i5 quad. The difference will be very obvious in each case in 80%+ of today's games. Especially in terms of the fps graph, smoothness and experience and to a significant extent in terms of median fps as well.
6. The Q9550 is unplayable in all games while the 3570k is playable. Isn't this a big enough difference? Besides, I guarantee you that assuming both CPUs get 40 FPS, the 3570k will still be a smoother experience.
7. My experience with old games back in the day, (present games of that time)
A643200 @2.4 to E4500
Huge difference even if FPS are similar or more. Though FPS were always more except with much higher settings on the latter.
E4500 to E7200
Minimum difference but could be felt by the naked eye at times.
E7200 oc to Q9550 stock/oc
Some difference in some games, no difference in others. Worth upgrading at that time but debatable VFM.
Q9550 oc to Core i7 860 stock
Significant performance difference, big jump, a lot more smoother and much better consistent fps, huge difference in fact with games of the period.
Core i7 860 oc to Core i7 2600k stock
Minimum difference at that time, barely noticeable. But of course things will be very different today and i don't regret the move.
Core i7 2600k 4.3 to Core i7 3770k 4.3
Never noticed a difference at that time. Can't say about now, but I really doubt it. I regret this move.