That is my RAM. DDR3-1333. 2 x 2GB ran at 1T command rate, but going to 4 x2GB drops the command rate to 2T. I have read that one losses bandwidth when dropping to 2T. Do I recover that loss with the increased amount of RAM? Was I better off with 4GB at 1T?
Don't get single sticks to create a pseudo Matched Set. You ASUS M5A88-V EVO can be touchy enough with some matched kits.
That said, the diffidence between 1T and 2T is more about stability than reducing any real bandwidth. On OLDER DDR 2 bit (prefetch buffer) and maybe DDR2 4 bit RAM there was a more noticeable difference, but DDR3 8 bit it's minimal at best. A bench like Super PI might barely notice the differences. Further, most all DDR3 1600 MHz or faster RAM is 2T.