Maybe they will, maybe they won't - even mixing 2 identical sets of the same exact model can be and often is problematic, mixing diverse sets, such as different models, freqs, timings, voltages, etc just increases the chances of problems which in some cases can be overcome w/ timing/voltage adjustments, but no guarantees.....Am working on an article for Tom's right now addressing this and a number of other common DRAM issues/questions