I've got Crucial ballistix ddr3 1333mhz Cas7 (but set at default 9)
Would these be good to overclock to 1600 mhz? and keep a highish Cas, instead of buying new RAM rated at 1600.
Another question on a related theme.
AMD phenom has a 1333mhz memory bus. So whether overclocked or standard, how does memory work at 1600, 2000 mhz etc on an AM3 cpu if the chip's bus is only 1333 mhz?
For such socket/cpu is all memory above 1333mhz actually an overclock for the system, if not for the ram itself?
More about :crucial ballistix overclock extra question
The default RAM speed is not necessarily the only speed that the IMC will function at. Any RAM speed above the default frequency is an OC. In order to run the RAM at a higher than default frequency you must change the BIOS settings. Some CPUs/RAM/mobos will play nice and run RAM faster than default but there is always a limit and with OC'ing there are no guarantees.
With DDR3 RAM, due to the higher frequncy and bandwidth upping the frequency or lowering the latency has minimal impact on system performance, typically about 1% unless you are able to double the frequency, then maybe you'd see a couple percent gain.
I would not suggest buying new RAM for a 1% or less change in system performance. Your RAM may OC to 1600 MHz. All you can do is try it.