Well, I'm fine so far. Milleinare and matmos really sucks up ram if i'm not wrong, so you prolly should take those away if you dont really use/like them.
My pc is freaking garbage. Win 7 ultimate, dual core processor (2.1ghz or something), 2 gb of ram and a 128 intel onboard graphics card.
My game only lags if i move through chunks way too fast, or when generating new chunks.