hmm depends, whats the rest of your spec like, if you got a quadcore (or 8 core) then gor either 8 or 16GB 1600MHz ram, id say stick to 8, however if your using a 6core processor then I believe multiples of 3 are better for ram, so for example 6GB or 12GB.
Harddrive is up to you, if you have a lot of assests that constantly need loading like I do with game design then SSD may be the way forward, however for now you may be better if you have a z68 chipset motherboard going for SSD caching instead, costs less and still performs very well.