Blimey tec4, you're saying 45/55 users requesting info at the same time sent things down!? That's quite shocking. How on earth do the likes of F.B. and such handle things. That's a bit of a depressing stat, but yes I'm sure there are lots of different parameters that could effect things.
I did also wondered whether the db 'queues things up', i.e. if there are 50 requests for the same data from different users does it do them one by one and make people wait, or just get overloaded with everyone 'speaking at the same time' sort of thing.
It's nice to know there are settings to control that, but I guess you need a reasonable element of control over your server, or speak nicely to your service provider, or get a better one.
Hmm, I feel some serious research is in order. It's a tough one to find much info about apparently without being a bit of a db specialist.