Confused by memory specs

[buzz_]

I'm looking to upgrade the memory on my ASUS P5K motherboard from 2x1Gb to 2x2Gb. The current memory is DDR2 PC6400, so should I just plug in more of the same, or would higher spec PC8500 give any benefit? Should I worry about the latency figures?

Video and photo work is my main power use. I am not gaming.

 

[batchie]

just buy 2 more 1gb sticks the same type you already have i have two setups both asus boards one with 2 x 2gb and my main rig with 4 x 1gb and i get a better overclock with the 4 sticks