Hyper 212 EVO will get you up above 4GHz but may limit you once you need to increase voltage.
Speaking of increasing voltage, what is your power supply? EVGA 850w gold rated PSU is not enough information. For example, the SuperNOVA G2 series is Gold and is great (although it's now outdated), but many units within the NEX series are also Gold but they're complete crap and would probably kill your motherboard if you tried to overclock on it. What is the model of your power supply?
Once these problems are out of the way, we can decide on RAM. From what I've seen (and I've done plenty of research), RAM speed does not have much effect on system performance. It seems the biggest limiting factors are disk access speed for general tasks that...