Needed emergency help

Only time hosting offshore would be more efficient, is if your host is very, very slow to begin with and you have a low traffic. High traffic like yours (which I am very impressed) would best be handled locally (preferred) or at least in the same network.
As a way to identify possible bottlenecks, only using site analyzing tools is the only real good way to do it. Since I didn't have access to your server (which is a good thing lol), I used http://tools.pingdom.com/ to test out your site, which is what showed me that the jQuery was the main culprit.
Best way to prevent your site from being bogged down, is to keep your setting low on many things that aren't really needed (aka, just fancy display stuff, like Members Online).
 
Oh, something that might help your site out a lot with the Members Online, is changing how long it takes before it checks to see if a member is actually online (for the jQuery load). I reduced mine down from 15 minutes to 3 due to the "ghosts" we were getting (it would show members who were online before logging in and then after logging in and was counting them twice).
 
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