What is the most sensible memory configuration

I plan to buy a ASUS A8V Deluxe Wifi-G and a Athlon 64 3000.If I understand things correct this MB requires memory modules in pairs. I now have one 512M Samsung PC3200 and one 256M Samsung PC2700and one 256M Apacer PC2700 (works fine on my current MB)I suppose I will need to get another 512M Samsung PC3200.What is then the best way to do?1) Only use the PC3200 modules to get max speed but only have 1 Gb2) Use all modules to get 1.5 Gb at the cost at running them at lower speed