reconciliasion :
depends what res your running/graphics...
you could run minecraft on minimum with 64GB's of ram and it would still lag.
its all in the game...
4GB of DDR3 at 1600Mhz would perform well in a vehicle simulator/racing game where theres cars and maps...
4gb of ddr3 at 1600mhz would just cope running a f-p-s like battlefield or crysis where theres explosions and lighting and bullets...
Do not listen to this person. First of all, you will rarely push toward 6gb of usage, depending on what you're running and to what extent. For a FPS like Crysis or Battlefield, what's more important is your GPU and processor. Effects such as gunshots, lighting, etc are handled by the GPU, so it's worth investing in products with good VRAM and such. Nothing under 1gb, and don't buy a product entirely off of its VRAM, there are other important factors in a GPU.
Do not use Minecraft as a benchmark for your computer's performance, that's just a completely awful idea. It runs off of the horrible platform known as Java, and should be shunned as a benchmarking tool of all things. This game would run at a massive FPS if it used the same languages that studio games use. You can get a crappy dual-core pentium to handle it very well.
Go with 4gb and up to 6 if you need to. 1333 or 1600 mhz will do fine, don't go higher than that. Processor and GPU are just (if not more) important in the end, sorry to say.