Try using
RMClock.
There are different profiles used by the program.
Performance on Demand is Cool 'n' Quiet. Then you can select a
Performance/Power Saving Preference. Setting this to
Power Saving Level 4 could perhaps help to avoid your
spiking problem.
Current official version of RMClock is 2.05. In the
Forum you will find 2.1 Beta-test release 2. This works very good with my Athlon XP-M.