database performance: Java Linux Databases: Hardware
It may seem obvious, but if your workload is I/O bound, then buying a faster CPU and/or more and fast RAM will do almost nothing to your database system's performance. Buying faster disks may be a better option.
It is also worth noting that a single shared server with faster CPUs will not necessarily be faster than a lower specced dedicated database server.
Here is an example of 4 vs 2 CPU cores (same clock speed) where the benefit is minimal (note: 1 of the 4 cores in the dual-core Opteron 270 system was under heavy load):
