I was wondering how far you could get stable on stock fan...i5 2500k

One of the key factors in a stable overclock (no matter how much) is a good aftermarket cooler. Low temps go a long way towards stability.

I agree 100% with Vedran. It will not work in that configuriation as I have tried it in the past.

I've been running 4 unmatched RAM sticks for months. Rock solid stable with the same DRAM voltage, same RAM speed, just had to slightly adjust the timings, but that's because the second set is rated 7-10-10-24 instead of 7-10-8-27Sandy Bridge is not so picky with the amount of populated slots.Anyway, 8GB is more than enough, and even though downclocking the RAM from 1600 to 1333 will have very little impact on performance, there will be some, so I would just run 8GB at 1600MHz