If all you need is more speed, I would put a reasonable SSD in as a boot drive, and put all the files on an ESATA or USB3.0 drive. that would stand to make the most diff. as for the RAM making a difference, it depends on what you are running at the same time. as for Gaming, is you are running nothing but the game, 4gb would be more than enough, but if you have other functions running at the same time, then max it out if you can afford it.
(I always say that if your operating system and hardware will take more, get as much ram as you can afford to put in. it cannot hurt!)