2000 below CL9 can get ridiculously good results. I suggest you test this via MaxxMem. 2V is not ridiculous for 1600 6-6-6, considering most RAM can't even do 1600 6-6-6. Just high voltage D9 ICs, they're completely safe at 2V if good heatspreaders are on.
Sure, CL6 is nice, but look at the bandwidth afforded by 2GHz RAM. I'll give up a little latency so I can push more data.
I guess at this level, I'm speaking merely of personal preferences, but on that note, wouldnt you want some headroom in your RAM? 2v doesnt leave much. If leaving well enough alone was O.K., I'd go buy a eMachine, but I like to push stuff. Just saying, I think the overall experience would be better if the OP got the 2GHz kit, or at the very least, something high performance that runs lower voltage.