I was wondering if i will notice a big difference from going from a old P4 2.8ghz 533fsb to a new Q9550 2.8ghz quad. and im talking about single treaded apps/games that will only use 1 core mhz for mhz is there a big differnce?

you would see a huge boost in performance even with single core apps.  

Of course there will be a huge difference, in any programs. Remember, The newer processor delivers greater performance at the same clock rate, in other words, more processing power per ghz.

http://www23.tomshardware.com/cpu_ [...] &chart=435

First off, there is nothing that only uses one core. While you are playing games etc, part of your P4b is busy doing OS tasks, plus whatever else you have in the background.
The big problem with your old chip was that it was bandwidth starved, the quad isn't, even with all cores firing.
The core2 architecture can throughput data more than 50% faster than your old chip.
Add to that that you will need a modern gfx card, and you have reached the shock and aww stage.
You will love it.

you will notice a huge difference

HUGE difference in anything that is cpu demanding. Stuff like web browsing, email and those kind off common things its no big difference. If you mainly do single threaded stuff and not a real big multi tasker, a higher clocked dual core will probally fit your needs better. Cheaper also.

one core will bottleneck your PC performances

Not only that but in order to go from a P4 (socket 478) to a Q9550, you will be using RAM that is about 400% faster and you will be using much newer and more efficient motherboards, and the FSB is alot faster and more efficient.  you will see an enormous difference.  like going from an 82 pinto to an 08 corvette.

even going from a P4 2.8Ghz to a 1.83Ghz Core 2 Duo you would see a big big change

Well... do you know the exact difference of the 2 CPU's you have in question?

You are comparing 2 Intel CPUs that are different architectures.  To show at least 4 differences:

P4 2.8ghz:

1.) can execute 2 instruction sets per cycle
2.) runs on 533 FSB
3.) either has 512kb or 1mb L2 cache (either northwood or prescott)
4.) single core

Q9550:

1.) can execute 4 instruction sets per cycle - per core (meaning each core executes 4 instruction set)
2.) runs on 1333 FSB
3.) has 12MB L2 cache
4.) 4 cores

Those are big differences, and are not apples/apples comparison.

Even an E2140 (1.6ghz) could out do a P4 2.8ghz at stock, simply because they do not run on the same architecture, so speed does not matter in this case scenario.

 
LOL thats like comparing a Taxi to Nasa's Space Shuttle
 
1 x Core2 core @ 2.4ghz = 1 x P4 core @ ~7.3ghz (superpi)

I have always said i wouldnt upgrade my cpu unless it was = or faster in terms of ghz, so thats why im considering choosing the Q9550. that and i want to make sure i have a cpu that i can hold onto for a few years 3-4 years.

More performance in terms of ghz is no longer applicable, ESPECIALLY when trying to compare a P4 with new technology.
The Q9550 you are looking at will be a huge improvement over your P4, simply huge. And 4 cores will go a long ways to getting years of use out of it.
 
The new processors do more work per clock cycle, much more efficient, and mutli-cored to boot. Your old P4 is completely outclassed pitted against them.
 
If you know anything about autos, it is kind of like saying I won't trade in my 72 chevy with the 454 cubic inch engine until they come up with an engine that has more cubic inches. There used to be an old saying at the race track, "there's no replacement for displacement". It is a saying forgotten now by all but the old timers, like me I reckon.
Engines now are half the size, use half the gas, a quarter of the emissions, but crank out the same horsepower.

**** the q6600 at 2.4 beats the **** out of your p4.  hands down

 
Clock speed doesnt mean jack

Herz is not a performance evaluating unit, it's a number of cycles per second
 
it just means that one processor has a given number of cycles per second
 
you can use it to compare 2 CPUs from the same serie (and even then, not quite...) such as the Pentium 4: a 2.8Ghz is better than a 2.0Ghz
 
but comparing a Athlon 64 3700+ at 2.2Ghz and a 2.8Ghz P4, you can't use frequency as a choosing factor: the 3700+ is better
 
it's because of the way the CPU works at the most basic levels
 
 
and even moreso since that the dual core processors have appeared: you can absolutely not use frequency to compare a single core and a dual core processor !

dont forget its also 64bit vs. 32bit

 
 
I'd say it is like a 1 legged midget in a footrace against a thoroughbred racehorse.

I went from a 3Ghz P4 to a 2.2Ghz e2200 and I saw a huge difference in Photoshop, multi-tasking, and the few games I do run. You just went from a Geo Metro to a Dodge Viper.

from white to black =P  
 
if u know what im sayin