Ive worked on smf for a few years now and notice the same issues you guys are having everywhere, mostly its the database size causing issues, try talking to your host about allowing a larger limit on the database connections to speed up loading times.
If you are getting 40-50 k views a day then that will kill any bandwidth you may have, google is horrible at bandwidth burning, there is a lot of options in the back end of the system for SMF for where google and other search engines can poke around in, setting limits on what forums they are allowed to see will slow down the amount of hits.
Worth a try is something you may have already done, Optimise tables in the database, clear site cache and run any security updates.
Nick