Mixing RAM timings and another question

Hi everyone.

I'm considering adding more RAM to my computer, but I just wanted to sort a few things out before I did. I currently have 2GB DDR2 RAM, with 4-4-4-15 timing (my extra question is about this, later on), and I'm wanting to add another 2GB RAM so that I'll have 4GB. I'm currently looking at buying this 2x1GB RAM kit, which has 4-4-4-12 timing, and also operates at 2.0V. Will mixing RAM like this cause problems? I can't find any RAM with exactly the same timing as my current RAM either, so if I can't mix the RAM, I might have to buy a whole new set of RAM...(any advice on this? )

Now my extra question... The motherboard I have is a GIGABYTE GA-M57SLI-4 Rev2.0, and the RAM I have is the OCZ FlexXLC CL3 model, however the CL3 comes from using an EPP feature on the motherboard, which apparently my motherboard doesn't have. But CPU-Z says otherwise - under the SPD tab, it says in the SPD Ext. box that I have EPP 1.0. Trying to set the CAS timing in the BIOS to 3 stops my PC from booting, so I have to reset the BIOS. I know if I try and use this with new RAM, then it definitely won't work, but I was just curious about this.

Thanks in advance!

Mixing RAM is not an issue. As long as the voltages and timings are the same it'll work fantastic (and even if they aren't, it's easy enough to change them). Make sure that your OS is 64-bit, as a 32-bit OS will NOT recognize 4GB of memory.

As for the second question, I'm not 100% sure, but I'm fairly certain CPUz just lists the compatible timings for the memory based on what the memory itself says it's capable of. Hopefully somebody can confirm/correct me.

That would make more sense. Every source I find tells me my motherboard doesn't support EPP.

That's the RAM I meant. But actually, it's currently running with 4-4-4-15 timing, like I said in my first post. My motherboard doesn't support the required feature to get the CL3 timing. What are the dangers of mixing RAM with different timings? And would you recommend I just replace my current RAM with some new ones? If so, I may just buy some cheap-ish CL5 2x2GB RAM. I'm not too worried about small performance drops, and I doubt the difference between CL4 and CL5 would be noticeable.

Thanks, that makes things clearer for me. I guess that's enough reason for me to replace my RAM! I don't really want to buy some RAM and then find that they don't work with my existing RAM, and then having to buy more RAM anyway.