ASUS board and compatible memory

Well thanks to many of you, I built my own PC a year or so ago. BEST THING I EVER DID so thank you so much for being there for me.

I have a quick question on an upgrade. I have an ASUS p5b deluxe board that uses ddr2 800 240 pin sdram.

I have a stick of corsair 1gb in there now and want to add two more. But they don't make the identical stick. Everything is the same with the exception of the timing.

The stick I have in there is 5-5-5-12
The new stick is 5-5-5-18

Everything else (speed, latency, capacity) are all the same.

I didn't know if I could have one stick with one timing and two other sticks with different timing. Not even sure that it means to be honest. Any help would be appreciated. THANKS!

Just another "bump" since it's been a couple of weeks and I am starting to think nobody may know the answer anyway. Anyone know if you can mix RAM sticks with all the same characteristics with the exception of the timing codes?