RAM timings
 

I have 1 stick of PC2-4200-444 and one of PC2-3200-333 running simultaneously, same 512mb capacity. Do the BIOS ram timing settings automatically adjust for the different clock speeds or do I need to delve into dark places to optimise performance?

They all go at the speed of the slowest stick on the system. :)

...so potentially better performance could be had by actually removing the slower stick, and having half the memory capacity running faster!
Fascinating. Some experimentation coming shortly!

Unless you're rendering large wire models or manipulating huge images I doubt you would notice any change by upping the ram speed. You will certainly notice a degradation by removing half the ram though. Really in most cases the computer is only as fast as the slowest part which is you on the keyboard or mouse. :)

Seconded. Halving your ram equals (in Windows) more page file access if you've only got 512mb, equals slower computer. ;)

Yeah, RAM is so slow compared to the CPU cache that the difference between the fastest and slowest memory timings available for a typical PC is only a few percent in peak performance. Swapping to disk due to not having enough RAM is millions of times worse.

SPD
 

There are settings in the bios to set the ram 'speed' but unless you have dabbled or overclocked everything is usually 'auto' and is determined by the 'SPD' data on the ram. These days it is not really worth faffing around with. Leave all ram in btw !