I've been reading some posts about adding new ram sticks and I found that the lowest timing one is the one that takes the lead. I also read that mixing RAMs with different timing and latency may provoke a system crash. But, does this happen also in dual channel MoBo's? Yes, the BIOS RAM settings apply to each DIMM.
For example, I'm using 2x2Gb KVRam 800 Mhz in a M4A758-M ASUS MoBo. If I want to add 4 Gb more, I have to use the same kind of RAM in order to get it to work? It is more likely to work than RAM with different specs. If you mix RAM, then enter the BIOS settings for the slower RAM. In either case, you may have to bump up the voltage on the northbridge (or it's equivalent) to get through POST and boot.
Or can I use a faster ram fruitfully? ??????