Expression Engine and PHP Version

Do you use EE at DH, and if so, which PHP version do you use?

I have two EE sites. They happen to be on different servers but they are both running mod_php 4.4.7. As of this past weekend or thereabouts, *one* of them has started throwing errors that appear variously as totally blank pages, or Error 64:host not available. EE strongly suspects PHP or memory probs but so far I haven't been able to get the actual PHP errors to see what's going on. The site is completely unusable and of course I'm two weeks out from a national meeting of the organization for which it's the member site. Murphy's Law, I guess.

DH kindly restored from a snapshot two weeks ago when things were working fine, but I still get errors galore accessing any dynamic pages. About half my Control Panel works. I can edit templates, but can't run utilities, publish, edit posts, etc.

Anyway, I can't remember *why* I needed this domain to be mod_php. I think I either failed to get EE working under PHP 5 back when you could toggle back and forth between apache module and php-as-cgi, or it might have been some other application I'm no longer using in that domain.

Anyway, despite the idiocy of making lots of changes when something very small has likely changed, thereby complicating the troubleshooting process, I'm tempted to try switching to PHP5. I believe that will be irreversible in the sense that I will no longer have the option of running mod_php if I can't get EE to work there.

Hence my question if you are happily using PHP5 with EE.