What kind of problems can come from mismatchedness?
What comes from mismatched brands and what comes if I mismatch latency and voltage?
I'm wondering whether it's just lower performance or instability/not functioning/something else.
the DDR3L vs DDR3 is a one way matching criteria. If your existing ram is DDR3L, you must get DDR3L when you add more ram. If you have DDR3 ram now, you can get either DDR3L or DDR3 when you add more ram.
Hmm... I don't quite understand this. Why does it make a difference what my existing ram is? If I can add DDR3L to DDR3 why not the other way around? The end result is the same, one DDR3 and one DDR3L.
The preference for ram is always to match the brand and model, but if that's not possible due to availability or price being too ridiculously expensive vs other brands. Then matching the speed and CAS timing is the next important one to watch for.
By speed you mean frequency, not latency, right?
What is CAS?
How can I find out what these other characteristics like CAS, latency, voltage (anything else?) are for my RAM?
Just get another 1333MHz stick as it'll downclock to the lower clocked stick anyway. Doesn't have to be the same brand, although note if it's DDR3L or DDR3 and be sure to mach.
I know it'll downclock, but as I may be buying used modules I may have to go for a 1600, so my question is would that mismatchedness cause any problems.