I run an Intel i5-2500k 3.3 on an ASUS p67 Extreme4
A year ago i bought 2x4gb GSKILL DDR3 1600 and only recently realized my cpu maxes out at 1333. However CPU-Z showed me running at 800Mhz and it has been that way since I've had them (a year with the BIOS setting on AUTO) with timings 9-9-9-28 and 1.5V. I then selected to run my ram at 1333 and my timings are now 8-8-8-24 at 1.5V.
Which setting is better?
Also I'm looking at potentially getting to CAS 6 or 7....could I OC my now declocked ram to 7 or would i be better off buying CAS 7 1333 1.5 and then OC'ing to 6?
What would yield the best performance compared to cost/effort?
1600 at 9-9-9-28 is plenty fast enough. You'll NEVER be able to tell the difference at 1333 at 8-8-8-24. Not faster, not slower (at least as far as you can "feel"). Don't worry about faster timings and lower speeds. It just doesn't mean much for everyday performance. If you were using a RAM disk, it would be different, but otherwise, not really much point, except for better bench scores.
What G.Skill Ram is it? Most Ripjaws 1600 RAM is 9-9-9-24 (mine is).