Depending on games you play. If you are not using all 4gb of ram during games you probably wont need to upgrade it yet. 1600mhz would give some some small speed/fps boost but not really as big as you may hope for. Also your motherboard and cpu have to support higher frequency.
For SSD in terms of FPS it should do nothing, SSD comes to play only when you need to load some of game data into ram. So depending on game if you are in game when you often have to load new data like new location or something like that it can help you but wont improve FPS. If you play some games when is whole level/zone loaded at start it will speed up initial load but will do nothing afterwards.
So for minor FPS increase memory may be better. But generally using SSD will speed up everything you do on PC, be it copy files, start games/programs.