Question about getting more RAM

[TotalNoob]

I currently have x2 Corsair CMX 512 3200XL sticks in my comp. Im gonna get another gig pretty quick. Heres the thing, Im getting conflicting advice from a couple friends. One guy is telling me to get the exact same type of RAM to fill out the other 2 slots on my MB. So, thatd be another 2 CMX 512 3200xl sticks. Hes telling me anything else can cause compatibility problems.

Another guy is saying I can get anything I want for the other 2 slots on my MB. So whos right? Do I have to get 2 more sticks of exactly what I have? Whats the best option?

Thanks in advance for any help.

 

[Sora]

Both are right to a certain extent. As you may have problems but usually, you don't.

As long as all the ram will run on the EXACT same speeds then you can go with 2 different sticks.

 

[augest]

Well, You have to get ram that your mother board supports... But also if you get ram that is faster then what you currently have your mother board will down clock it to the same speeds as your current ram...
It's best to stick with the same ram.