CMS thread processes on webserver maxing out CPU for my forums/CMS
 

yesterday i had a large number of users (around 125) try to view my CMS/forums at the same time. during development the most that we've ever had has been about 5 users, and never any problems. Using 4.0.2 PL4 CMS + forums. and when we gave the URL out yesterday, the server came crashing to a near halt because CPU processing power was maxxed out. I have always used vbulletin and have never had this problem but the host says that the thread processes are using about 23mb per user, which seems rather large to me. They physically showed me the thread process list so I know this to be true.

What can I do to limit the size of CPU usage? Does using file attachments in database increase this? What else can be done to optimize? The site is using about 3x the CPU usage of the other major site on this particular server... and I cannot afford dedicated or load-balanced hosting.

Is there a list of optimization things? This is pretty critical for me as we were planning to move over tomorrow and cannot.