May I ask you a simple question? Why should I overclock the hardware for the software released in 2006? It seems that you all, folks, lost a common sense. 
Ok, fair enough smarty pants, let me ask you some questions before I answer yours since you generally seem to be argumentative, lol.
Why would you put any money into a sim (FS9) that was released in 2003?
Why should you buy aftermarket airports when FS9/FSX already comes with the same airports?
Why should you buy after marker aircraft when FS9/FSX already come with them?
Why should you buy GE Pro, GEX, BEV, or any photoscenery when FS9/FSX already has ground textures?
Why does anyone do anything to thier computer at all like add a better video card, better RAM, etc?
Enough?
Ok, the answer to all the questions I asked is the same, because it makes the sim look better and sometimes perform better.
Same reason why you overclock, because if its done right, it allows you to run the sim better and faster, thus giving you more headroom to add more autogen, scenery, AI, etc. It's no secret that the MS versions of FS have always been hungry for core clock speed.
The same thing applied years ago when FS9 first hit the market, a lot of people couldn't run it very well on the single core machines at the time that were running stock in the 1.X to 2.5ghz range and like you they refused to go to FS9 and stick with either FS2000 or FS2002. Finally, like with all the past versions of FS, it took time for hardware to catch up. It wasn't until around 2007-8 when hardware caught up that allowed FS9 users to really run FS9 at high levels with no overclock, so that was about a full 4 to 5 years. Until that point a lot of folks had to OC their single core Pentiums to get the most out of FS9, now you dont.
Pretty much the same thing applies to FSX, except that now chips aren't getting a whole lot faster as far as clock speed, but more cores are being added.
Like Umberto said you dont NEED to OC, but I can tell you from my personal experience it sure made a HUGE difference I my machine, but like everything in life, what works for me might not work for you.
We all know by now, especially if your the same Dmitriy that posts on Avsim under the username G-YMML1, that your not much of a fan of FSX and have no intention of ever switching to FSX, at least not for "IFR" flying. So if that's the case why keep pestering those of us that like it or use it?
No one is trying to twist your arm to get FSX or overclock your computer, it only came up because newmanix spoke about it so I offered my opinion, so why bother with the comments? Just stick with FS9 like you already have and you wont have to go thru the trails and tribulations of setting up FSX and getting it to work well on your computer. For others like me, it wasn't a whole lot of work and for what little tweaking I did, its paying dividends.
BTW, please don't question our common sense, especially when you didn't even phrase your last sentence correctly when you questioned it :-)
