Ye, i noticed it alrdy, 2 much images are there which is slowing the page speed little bit, i would not teach you anything buddy, but at least i think that you should try to setup some caching "tools" on server, like nginx and varnish, and at least try [URLnf="http://www.maxcdn.com/solutions/cms/vbulletin-cdn/"]MAXCDN[/URLnf], much better than Cloudflare for caching, it costs little bit, but enough to keep good pagespeed loads on your projects...
On your place, i would setup Apache2 + nginx (look around for best configuration for vbulletin), then optimizing the mysql (recommended to do this), and at least MAXCDN (for the win).
Thats was now about optimizing the server & network, now the best thing what you can do after you finished server/caching optimization, its to deinstall useless plugins on vBulletin, there are some optimization plugins such as Compress forum templates, template cache system, and realtime page compressor for vBulletin, but at least i never tried them, so as first research little about them.
And the final work should be to optimaze whole Template (html, css...)
And just to let you know, it depends on your server performance to, i mean for such big forum with huge amount of daily traffic i would use min 12gb of ram and Quad-Core CPU, and ofcourse the server should be on 1 GBit/s-Port. I have tried alot Hosting companys, where i had my own Dedicated servers, but at least my favorite is Hetzner.
(I have an friend who is runing vBulletin, and sometimes he is coming up to 3k visitors, + there are tons of images linked, and with the configuration which i alrdy wrote he dont get any problems, and i must notice that his users cames specially from USA and Asia, and still he is satisfied with Hetzners network speed)
And look for SSD disks, this is today MUST-HAVE.