Everything is fine - cron runs, site reindexes, performance is good.

Turn on Porter-Stemmer and I have chaos.
-Cron fails (I get the exceeded time limit error).
-Site won't reindex.
-Performance when navigating through content or accessing admin functions is poor.

Turn off Porter Stemmer and the site returns to normal behavior.

I looked at "#361171: Cron doesn't run if search module enabled" but Search isn't an issue - Porter Stemmer is. gdips' approach mentioned there isn't valid for us - the site must be indexed (and we have no php content in nodes). A related issue is described at: http://drupal.org/node/436028 - however, that thread does not really describe the issue I'm having.

Note that Pingback is not installed.
Also note that Poormanscron is installed, and works wonderfully until Porter Stemmer is enabled and the site is set to Reindex.

I have not followed Mojah's suggestions on http://www.mojahmedia.net/drupal-cron-run-failed-cron-busy-probably-stuc... as that has received a mixed response from posters elsewhere (delete sempahore and cron last) but I will do it if others feel there's really no harm trying it.

Any suggestions?

Thanks, pV