Actually Pat, my 'disk performance meter' as well as my Win Task Manager activity levels have ALL been greatly reduced since I began off loading all VSTi's to a dedicated machine. Now neither machine is being taxed high, as with my main machine 'was' when I had my largest of projects since I began increasing VSTi usage. At that time, when my overall usages started exceeding my machines capability, what I was experiencing was that, between my audio & midi tracks running 3d party VSTi's, my tracks began to sound 'out of alignment' & 'drifted'... that was a very strange thing, but again, only this only happened on the heaviest project I've ever done, while my other projects played fine.
Keep in mind, I'm talking about a Win XP 32 bit machine with a quad core @2.5 GHz CPU & 4 GB installed RAM, and my latency set to near the lowest setting. I don't THINK this had anything to do with 'HDD Cache' per say, but was an overall limitation of the machine as a whole. Though I believe my 'disk meter' and 'Win Task Manager' indicators were very high at that time....and raising latency helped when that happened. My VSTi only machine is exactly the same as above, in which I now bounce to my audio machine after I'm done working all my midi tracks & VSTi assignment.
Ok, if I'm absorbing correctly... I take it (my mobo uses up to standard SATA 2 HDD's) for an OS it's best to have at least 16 MB HDD cache, and for a Samples HDD, at least 32 MB.
Again, I'm not looking to 'replace' my current HDD's, they're working... I'm planning on buying 'spares' to have on hand. This go's for everything else, I've been collecting spare 'everythings' actually.