>> a single page load was maxing him out and after a single page request he was having persistent high I/O and CPU activity and this was true even with plugins disabled.
Enable the mysql slow query log.
log-slow-queries = [path to the log file]
That should reveal the slow query issues.
Most blogs will not have enough content to even slow down a half way decent server on a select * from wp_post type query.
The problem with innodb is that it does require a fair bit of tweaking - far more than MyISAM and is non-trivial, specially if you're not technical enough to drill down the code or the query that is causing the slow down.
InnoDB shines in high concurrency situations when tables are being hammered with updates. In MOST situations, myISAM works perfectly and is much more suitable for anyone who classifies themselves as a webmaster, as opposed to a database admin, IMHO.
If by chance you happen to be running PHP-FPM instead of mod_php in apache, take a look at the PHP Slow Query logs too.
request_slowlog_timeout - The timeout (in seconds) for serving of single request after which a php backtrace will be dumped to slow.log file. Default: "5s". Note: '0s' means 'off'
slowlog - The log file for slow requests.
>> shri! Goodness, haven't seen nor heard from you in years. Welcome back.
Lorax, I visit atleast once a day... but rarely have anything to say. :)