I have a Corsair DDR3 2x2GB kit running at 1600mhz 8-8-8-20 4-11-5-4.
When I'm doing the Sandra memory bandwidth benchmark, i score 12.86 gb/s, which is lower than another rig with 1400mhz and 9-9-9-24 timings...
Mobo: Gigabyte 790FXT-UD5P
CPU: Phenom II x4 955 oc-ed to 3.6ghz
Memory: Corsair CMX4GX3M2A1600C7 2x2gb kit
Another question if you don't mind...do you lose your warranty if you increase the voltage of memory modules? It's currently set at 1.65v, which is stock for them..
You know, in the end it doesnt really matter..... Memory bandwidth differences only show up in benchmark apps, most of the literature shows no differences in games or apps... The same literature shows in benchmarks that getting the latency down is better than higher bandwidth (1600MHz) - but again - its on the order of 1% or less...
Although I'm inclined to agree with vvhocare5's point that you're not going to notice much of a difference in every-day use, I do sympathize with your concerns. 99% of the fun of this hobby is tweaking this stuff to perform to the maximum possible level of performance and reliability. I wish you luck in getting this up to the bandwidth target you're seeking and wish I had some better answers.
From what you've said about your voltage settings and the level of performance you're able to get, I'd suggest that you have a couple of below-spec memory sticks. You might consider trying your luck at an RMA -- you have a good excuse; you are giving it the voltage it wants and the timings it wants. It should perform at -- or even better than -- the specifications given by the vendor. If they're not, not your fault or the mb's fault -- the process of memory speed spec'ing (namely, binning) has the potential to be fraught with error and imprecision, so getting out-of-spec ram is not impossible unless the vendors are exercising the height of rigor and discipline in the binning process.
Given your experience, they clearly aren't. You've done all you can. RMA time.