Note that the more RAM you have, the less it will run over spec-speed.
I have about 20 of those really extreme SIEMENS DIMMs here and a number of those Infineon ones too - the very same ones. They do rock.
BUT bear in mind the following when making a choice:
If you have two of those 64MB (or a 128MB stick) you will NOT get the same benefit. You will make maybe ~125Mhz - The amount you can go over the "rated" spec depends on:
1. The total number of memory chips (on all active/installed DIMMs) - more chips, less OC.
2. The number of DIMMs, more DIMMs/slots, less OC.
3. The total amount of Memory - more RAM, less OC.
One example of this when not even OCing is when I install 3 el cheapo PC-100 8ns DIMMs in my PIII desktop, the machine wont even POST. It will not even power up, it'll sit there and beep a few times and go quiet. These 3 PC-100 DIMMs wont even run at CAS3 on 100Mhz.
They are Mitsubishi, made in 1999.
Generally speaking, if you have two CAS3 sticks, each capable of CAS2 at ~130Mhz, putting them both together you might not make CAS2 at 100Mhz anymore. Some work better than other and I am sure it also depends on the motherboard.
This has the side effect of making harder to push your FSB with 256MB of ram than with 128MB than with 64MB. I bet some people with 128MB could achieve even higher speeds with only 64MB.
For UNIX/SETI machine this would be a MAJOR boost.
You could probably OC like a mofo from hell with 32MB CAS2. I have an IBM CAS2 7ns DIMM, and I hit 150MHz with it - it the MoBo and the fact that I cant run MS Windows with only 32MB that prevent me from using it.