I just want to know which ram is going to be faster
my choices are  
 
a-data 800 mhz 4-4-4-12  
http://www.newegg.com/Product/Prod [...] 6820211282
 
or  
 
G.Skill 1066 mhz 5-5-5-15
http://www.newegg.com/Product/Prod [...] 6820231166
 
I have both at the moment and need to RMA one so let me know which one is going to run faster. I don't care about the price I will stick to the 1066 mhz if it will run faster
 
I am running an e8400 on a p5k-se
evga 8800gt
barracuda 7200.11 500gb 32mb cache
raidmax smilodon case 500 watt PSU

I only say 800 because there are known compatibility issues with 1066 DDR2 and most chipsets.  I have no knowledge as to whether or not X38/X48 are affected though.

the 1066 is working in my p5k-se very well it is very stable (72 hours prime95) with 0 errors.

The difference between 1066 and 800 isnt noticeable
 
if u want to OC i say go for the one which has lower timings

I will not be overclocking

So it wont make a difference u will never notice the difference between 800 and 1066 in real world apps/games

I would choose the A-Data 800 ram because it has faster base timings. Besides, 1066 is often just 800 that has been overclocked with a voltage increase from the factory, but that does not mean it will run that fast in the individual computer.

I can't tell for sure about the timings, because I don't know what the timings are for 800 speed on the 1066 memory.
Like others said, go with the A-Data since you are not overclocking and it's also cheaper.

cpu-z reports the ram as pc2-6400, so the ram is running at 800 mhz. This is on windows xp pro

You have E8400 and do not want to OC at least up-to 3.8 GHz ??
Anyway it's your call
In this case you don't need 800 RAM  
You need 667 as FSB of this proc is 333
But anyway I trust G.skill name more

The PC is basically a workstation, I don't play much PC games. I prefer to get the longest life out of my hardware and to preserve manufacturer's warranty which is why I do not tend to overclock.

@OP:
If you are planing on getting RAM natively higher than DDR2 800 be aware that there are compatibility issues. Many users reports and my personal testing has shown that there is a very good chance you will run in to issues with RAM higher than DDR2 800, such as DDR2 1066. I recommend you get quality DDR2 800 RAM and run them at 1:1 ratio (for FSB 1600) or overclock the RAM. This issue dose not apply to DDR2 800 RAM that has been overclocked.

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E2180 @3.2Ghz + P35DS3L +8400GS (700/475 OC)  

I am currently running the 1066 and there are no computability issues, it is working great,