[ic] Time for new hardware?

[Grant]

I've been making a lot of optimizations lately and I think I'm to the
point where my 4 cores just aren't able to keep up with demand during
peak traffic hours each day.  Pages load quickly when I see fewer than
4 busy interchange processes in top but things slow down drastically
after that.  Once I'm OK with the degree of optimization my ITL pages
have undergone and I'm not IO-bound or memory-bound, is it time to
throw CPU at the problem?

I'm a little puzzled because I've seen my server perform much better
under much greater loads in the past.  I thought my growing mysql
tables could be the problem so I set up indexes and it has helped but
my server still struggles under loads it used to handle without issue.
I did notice that my tables are split about 50/50 between InnoDB and
MyISAM and I'd like to make all of them InnoDB.

- Grant