What kind of budget are you on? Are you OK using liquid cooling kits (like Corsair Hydro series, for example) or are you just wanting air only? Air will ultimately give you less problems, but could limit choices for RAM. Also, what case do you have?...just want to get an idea how much room you have to work with.
Regarding RAM, I remember reading a blog from Corsair not long ago that showed high-speed RAM making a substantial improvement in BF4. TBH, it's just one game but may be something to consider if you find a good deal on a high-speed kit. In general, however, I wouldn't make a point of looking for something like a 2400 MHz+ kit as most games don't benefit. DDR3-1600 or 1866 is good for most gaming rigs, IMO. I've had lots of kits from G.Skill and they've treated me well (this
might interest you)...but in general most stuff from Corsair, Patriot, Mushkin, and Kingston will be good.
With the fit, the RipjawsX are low profile enough that they shouldn't interfere with some of the bigger air coolers out there. I ran a set of RipjawsX with a Noctua D-14, for example, and had no troubles with it fitting.