Do you have a host or are you hosting yourself? If you're getting overloaded on an 800 mb database it might be a poorly coded mod or bad settings- have you looked up optimizing your server for vbulletin?
http://www.vbulletin-faq.com/optimiz...tin-server.htm
https://vborg.vbsupport.ru/showpost....8&postcount=15
Also see dedicated forum here:
http://www.vbulletin.com/forum/forum...-Configuration