Why won't my RAM post at CAS3?

[HangTime]

Bit of a strange one here. I was doing some testing last night of high FSB on my ancient Twinmos PC3200 2*512meg kit. As I was going for FSBs in excess of 250mhz (DDR500), I was trying CAS3 to start with to see what she could do. However no matter how loose I made the other timings, I couldn't get the system to POST.

Now this is where it gets a bit weird. The system will boot up fine using the same settings, but at CAS2.5. This doesn't make any sense to me, why would it run Windows at CAS2.5, but not even POST at CAS3? Surely it should be the other way round if anything, with lower latency proving more unstable/usable.

 

[HangTime]

Is there any tool which can query my RAM to find out what chips it's using? Twinmos from that period is often bh5/bh6/ch5/ch6 I believe.

I tried looking on the chips last time they were out of the pc, but the writing is so small, and contrast so poor that I couldn't make out what it said with my crappy eyesight.