For everyday performance I'd stay at 1600 @ 7-8-7-1T. There is a nice explanation/guide to calculating the best scenario for particular benches here
(Ian Cutress/AnandTech). Generally, single-word performance is more important to apps that do a lot of cache swapping and to highly-parallel simple-data calculations and lookups (like database operations or WEP/WPA cracking/phone unlocking). Multi-word performance is important to intensive GPGPU work, most games and complex-data crunching.
Using RAM as a RAMdisk is about halfway between, because you're doing both random reads/writes (browser cache) and sequential ones (when there are larger chunks of data like large pics and video streams). Though, in both cases, the RAMdisk will outperform any form of non-volatile storage by a large factor, no matter what your RAM settings are.
AIDA's memory testing is done pretty well.