I'll buy a kit later, i'm just using some parts I had laying around. It's not my main rig, I had some parts scattered around and I'm just building for fun, do you know if there's a higher risk of OCing? Or can I even OC different modules? I'm kinda rookie...
If you have them onhand, there's no risk in trying. Worse that'll happen is either you won't post with both installed, or you suffer a bit of instability. Running at stock 2133MHz, you'll
probably be fine, but it's not guaranteed.
As far as overclocking....
Mixed modules will almost always have different subtimings, which can be problematic. One will be "better" than the other, and you'll have to match timings appropriate for the 'worst' of the two.
Then, there's a matter of the specific modules themselves.
Generally, if a module (or even a kit of 2+ modules)
can clock higher with reasonable voltage/timings, they'd be sold as such.
2133MHz modules/kits tend to be the lowest performing chips, necessitating excessive voltage or extremely loose timings to get them to higher clocks, assuming it's possible at all.
Again, that's a generalization, and some 2133MHz modules/kits
can clock higher with relative ease, just don't expect phenomenal results. If you can push a 2133MHz module/kit to >2400MHz without going crazy on voltage, or extremely loose timings.... that's a win.
Thanks for your response. What do you mean with optimally? Is it better to just use the 8gb one rather than both?
For optimally, I mean you
may suffer random instability that can be near impossible to pinpoint.
As for better using 1x8GB, no, beyond the slight risk of instability.
Are you using Intel or AMD?
AMD, you forgo dual channel outright if you're not using 2xWhatever GB.
On an Intel, you should benefit from "flex mode" meaning (essentially) the 4GB + 4GB (of the 8GB module) will 'work' in dual channel, and the balance (4GB) will be single channel. I'm not sure of the performance difference in that regard, but it's going to be better than 1x8GB, worse than 2x8GB.