Thanks for the gr8 answer Unixlord, if my PC wouldn't have ran fine for 6 months with Vista I would choose another OS, but I have no reason to do so. I was just asking a simple question because I'm not absolutely sure if my RAM gives 100%.
According to everest my modules support 4-4-4-12 @ 533

and yes it was as cheap as it could get ($80-90 for the 2 sticks).
I've made a ~6 hour test with memtest and it ran the tests 8 times and it showed 6 errors. I've set the Address Range to test the whole memory, I don't know if this changes anything but it's not the default setting.
All the errors are the same except for the mem address: Good: 00000004; Bad: 40000004; Err-bits: 00000004. The address is usually around 1GB and above 3GB.
I will test the sticks one by one and I hope that it's not the motherboard. I would hate to remove it.
Honestly it's pretty hard to setup the BIOS properly, so it won't cause any booting/restarting issues but I could do it once (goddamn crashfree bios lost settings a week ago).
Thanks for reading!