R9 280x + 4GB RAM + 120GB Intel 530 is the best if you can afford it ^^
SSD will not get any extra fps in games but will make your PC feels more responsive. Get it only if you really have the money.
I saw also that you have only 4GB RAM, an extra 8 (2x4) or 4 ()2x2 GB more RAM should bring also quite a lot.
If you can do some replaning, I would suggest to get 4 or 8 GB more RAM (not GPU RAM)+R9 280x, and postpone the SSD.
This should be the better upgrade for you.