Many of the Dell's cannot be overclocked.  If you want a PC to Overclock look at the Alienware line.

This is the way it's been for a long time.  I think some of the XPS models could be overclocked but since Dell bought Alienware the gaming/overclocking focus has been on that line.

As far as Intel promoting overclocking, I have a home built using an Intel DP35DP motherboard and a Q6600 processor and the Intel M/B does not have any provisions for overclocking.  

The reason I didn't buy an alien ware computer is because:

A) They are extremely overpriced

B) ALL of the computers there have 3D enabled graphics cards, so I'm paying extra for a gimmick that I'm never going to use

The XPS 8300 has Intel Turbo Boost Technology, which will "increase processor frequency dynamically until the upper limit of frequency is reached."

Not exactly the same as OC, but it's something... 

NOPE.AVI-

No you cannot overclock the processor on your Dell computer. The Dell BIOS is
proprietary and has no provisions for changing the multiplier or any other
method frequently used by overclockers. Typically, overclocking causes the CPU
to produce excess heat, and without special cooling devices, this can shorten
the lifespan of, or even permanently damage the chip. Because of this, I'm sure
Dell doesn't want you trying it.

And yes Intel does have two newer CPUs which are made for overclocking, and it is
even (somewhat) advertised and encouraged by them. They are the i5 2500k, and
the i7 2600k. Notice the "k" at the end of the number identifier,
which refers to the unlocked multiplier which can be accessed in the BIOS.
However, neither of these two chips are available in a Dell XPS model (or in
any regular Dell). Only the non k versions of the i5 2500, and i7 2600 are
available in Dells. They are not meant to be overclocked, but it is possible to
do so using different methods on certain systems. However, you cannot overclock
them at all on a Dell.

There are a few Alienware desktop models available here which do offer a factory
overclocked Turbo Boost feature, some going over 4GHz. This is not the same as
having the multiplier freely unlocked in the BIOS however, as is preferred by
those enthusiasts who overclock. It would seem that Dell is not quite yet
comfortable with allowing their customers to play around with the core clock of
the CPU's in their computers. Understandably, it would potentially increase
returns and exchanges for burned out/damaged CPUs, by folks who were either too overzealous,
or just simply didn't know exactly what they were doing.

But I wouldn't worry too much about it. If you have the system at the top of the
list as you state, you have a very good computer, with a blazing fast CPU. And
the 6770 is a decent mid-range card. With that combo and 8GB of RAM, you can
run ANY current game on med-high settings.

Studio XPS 7100

AMD Phenom II x6 1090T

8GB DDR3 RAM @ 1333MHz

Western Digital VelociRaptor 7200RPM 1.0GB HDD

HLDTST6X DVD+/-RW + BD-ROM

XFX Radeon HD 6950 2GB “XXX” version

Corsair TX650 watt PSU

LG M2262D FLATRON HD 1080p monitor _____________________________________

Incorrect - as far as OCing an Q6600... The stock Dell XPS series with a 2.4Ghz Q6600 can be easily OC'd to 3.0Ghz, then using a little app called SetFSB you can go to at least 3.2Ghz as I have done.  The Q6600 was built with various freqs, Dell use the basic 2.4Ghz setup. There is a Facebook page for Dell XPS 420s within which I detail how to do all of this.

I have an ati graphics card in my i7 xps 8300 and what I done was downloaded the catalyst control center of the ati radeon  once it is downloaded right click your mouse and it will be there open it go to performance and there is a few things you can make faster like the gpu clock settings also the high performance memory clock settings and you can even make your fan go faster or put it to auto or manual hope this helps you out it did for me see yaaaa