If performance is still a problem (some time) after the second
computer is installed, there's at least one other approach that
I haven't seen emphasized here: throw RAM at the problem.
If one of the systems shows any significant paging, installing
lots of memory (so the whole DB is in memory)
is likely to make things faster.
Even relatively low-end machines have really impressive database
stats when EVERYTHING runs out of main memory :-).
Hopefully, the second machine will make all this unnecessary.
I just thought I'd post a few ideas as I think of them.