What about your apache daemon?
I told you, that it is a bad idea, running mysql under heavy load and an apache on the same machine.
Did you take a look in your slow queries logfile?
If you calculate your cache miss rate, you will see, it is _very_ low. But, if you think about, it is not so low because of not having enough memory. It is so low because of the missing indices.
Please note your "Select Scan" and your "Select full Join" values. They are to high!
Your problem are not the buffers of MySQL, you should optimize the database structure.
So long...
Indy