Proper Disk Cache size in OS9?

[Small Moose Ltd]

According to my 'Sam's Teach yourself Mac OS9 in 24 hours' book, the default
cache size is 32k of cache per Mb of ram.

I've got 320Mb of ram, so my cache should be set to 10240k correct?

When I check in the memory control panel, it is set to 8160k

If I increase the memory, will this make my iBook more efficient, and less
prone to spinning up the hard disk?