Don't count on overclock, that can be done only in limited number of combinations and involves higher priced memory. Safest way would be to look at memory QVL and choose any available or cheapest with 3000 - 3200MHz. 3200MHz is a sweet spot for Ryzen.
All DDR4 RAM starting frequency is 2133MHz and everything above that is considered OC. Numbers higher than that are actually XMP (eXtreame Memory Profile) that particular RAM is rated for. As is is also OC, overclocking over that is overclocking the overclock. If it was possible in all cases they would just rate that same RAM higher (and charge more).