Even I used to think like this when I was a kid. 
But from experience I can tell you that even when a Q9550 and i7 860 give similar average FPS, or even close minimum FPS, that doesn't mean that the experience will be the same.
Although the FPS increase in going to Core i7s was just like 20-40% in game, the actual difference is much more.
Games will stutter and lag on a Q9550 even with 60 FPS, and the gameplay won't be smooth at all. However, things will be butter with SB at the moment.
I went from a Core i7 860 @ 3.675 to Core i7 2600k at stock and in some games I did notice more smoothness and better gameplay, despite almost the same FPS, things became much smoother and quicker!
And this is despite the fact that I had 8GB XMS3 dual ch RAM throughout, that too DDR3 1600 Mhz.
So nothing but the CPU caused the difference.
And this is the difference btw a SB and Core i7 and presently can be felt in only 10-20% of the games if not less. But 95% of the games can feel the difference btw a Q9650 @ 4+Ghz and a a core i7 at stock.
Similarly, dual cores can't be used any longer, and they were really new back in 2006/2007(C2Ds) but by 2008 late/2009 beginning, they weren't up to the mark.
The moment Intel launches 8 core Ivy Bridge, in at most 3-6 months you will need to upgrade, and you will feel the need even sooner
But from experience I can tell you that even when a Q9550 and i7 860 give similar average FPS, or even close minimum FPS, that doesn't mean that the experience will be the same.
Although the FPS increase in going to Core i7s was just like 20-40% in game, the actual difference is much more.
Games will stutter and lag on a Q9550 even with 60 FPS, and the gameplay won't be smooth at all. However, things will be butter with SB at the moment.
I went from a Core i7 860 @ 3.675 to Core i7 2600k at stock and in some games I did notice more smoothness and better gameplay, despite almost the same FPS, things became much smoother and quicker!
And this is despite the fact that I had 8GB XMS3 dual ch RAM throughout, that too DDR3 1600 Mhz.
So nothing but the CPU caused the difference.
And this is the difference btw a SB and Core i7 and presently can be felt in only 10-20% of the games if not less. But 95% of the games can feel the difference btw a Q9650 @ 4+Ghz and a a core i7 at stock.
Similarly, dual cores can't be used any longer, and they were really new back in 2006/2007(C2Ds) but by 2008 late/2009 beginning, they weren't up to the mark.
The moment Intel launches 8 core Ivy Bridge, in at most 3-6 months you will need to upgrade, and you will feel the need even sooner
etc etc. see some reviews.
