It depends on the games in question. There are cpu bound, gpu bound, ram hungry, and combinations of those three.
Your setup is weak overall, so if you get a Ryzen 2600x and keep the GT730, but play gpu bound games, there will be next to no performance increase due to still being gpu limited.
Same result if you were to flip it, say an RX 570 and keep the FX 6300, but play cpu bound games.
You should plan to upgrade everything at once. Upgrading one or the other will just lead to a lopsided build with little gain.