Funnily enough, before I got sidetracked on discussing my big ego with a disgruntled member, I started typing a post about how many PMs were flying through the system (noticed due to the email notifier going mental). 31 members online, 9 at that moment sending PMs. I'm amazed at the numbers being sent, and surprised the system can cope as well as it does... ...but then I knew it would, my over inflated ego told me

Right, we are having some server capacity problems, but there are some upgrades happening over the next couple of weeks. After that, once we have another baseline (basically, know/understand how/why its performing), we can look again at modest increases (though will probably happen a 1 extra PM per hour type thing).
2 things we potentially could do are:
Restrict the number of emails the system can send per minute (reducing the processing overhead for a given timespan, but potentially creating long queues for the email notification system)
Reduce the size of PM inboxes (reducing the processing overhead for the database, as the database will dramatically shrink)
I do know any limits are frustrating, and am embarrassed we're unable to provide a (stable) system without such limits
