Just spent an hour or so tweaking the server running DaveProxy, mainly the introduction of mod_perl and a couple of little tweaks to Apache. Both together it should help keep it up during the worst periods of traffic.
I decided I'd take this course of action rather than moving over to PHProxy, although CGIProxy is very heavy on resources, using mod_perl should cut out the perl interpreter instantiation for every request and also allows easier monitoring using Monit. While PHProxy is better on the resources side of things, CGIProxy handles more features.
Depending on how well it goes over the next week, I may introduce squid as a cache between Apache and clients.