It depends on what part of the system is currently the bottleneck and how
much you want to spend. Since the target is the CPU and I/O, we assume
you're already using EtherTalk and not LocalTalk. This is the most
obvious first step to improve performance.
The next step depends on what the most important application is on
the server. Upgrading the CPU from a Macintosh II to a Macintosh IIfx can
help a number of server operations a little, but it won't make dramatic
differences. If a high percentage of the server's time is spent waiting
for the disk drive to complete seek operations (such as with multi-user
database applications), then speeding up this waiting won't do much good,
and you should consider a higher performance disk drive. This may consist
of a disk drive with faster seeks and throughput, but could also be
a caching SCSI card such as the DayStar SCSI PowerCard with several
megabytes of cache RAM. Each contributes unique advantages.
A combination of all of these upgrades would give the highest performance
improvement. Since we haven't performed any benchmarks on this subject,
we can't provide you with real numbers for comparison. Our recommendation
is to obtain a caching SCSI card for evaluation and decide if it provides
the necessary performance improvements.