Matching Memory question

Getting ready for my major rebuild and here is the question. A few months ago I needed some more memory for kids computers. so Instead of buying memory for them I bought new memory for me and handed down my then current memory.

The old Memory is:
OCZ Enhanced Latency 1GB (2 x 512MB) DDR400
Cas 2, 2-3-2-6, 2.6V

The new memory is:
OCZ EL Platinum Revision 2 1GB (2 x 512MB) DDR400
Cas 2, 2-2-2-5, 2.75V

During my rebuild I will be rebuilding the kids computer also. The older OCZ memory I do not need to use on their computer.

So, now to the actual question> Can I or should I use the old memory in conjunction with the new memory on my new MB giving me 2 gig? Or should I just stick with the 1 gig of the newer memory?

The new MB is the ASUS A8N-SLI Premium NF4 and the CPU is AMD 64 3700+ san diego.

If you are going to overclock then I don't believe that you want to combine the two.

The newer stuff uses the Samsung TCC5 chips and is capable of high overclocks, near or beyond 300 HTT if you have a good set. The older OCZ uses either CH-5 or maybe ProMOS or Mosel chips and is not capable of the same kind of high clocks as the Samsung. You would end up dragging the new stuff down.

I was afraid of that.

Well, I do have another question. What approx should I expect to be able to run fully stable with the following?

ASUS A8N-SLI Premium NF4
AMD 64 3700+ san diego
OCZ EL Platinum Revision 2 1GB (2 x 512MB) DDR400
Cooling:
I will be using the Thermal Take Big Typhoon and my case has 7 80mm fans.
Power will be the OCZ modstream 520