When was the last time you updated your addons? Running outdated addons can easily cripple the performance.
I'd try disabling them, and if it does help, enable them 1 by 1 to find the culprit.
Bah, all the related posts I read where folk recommend turning them off, and I didn't bother. Running with 0 addons gave me 79fps from 18. You're my personal hero and savior.
When I find the addon that's diving my frames, is that just one that I can't use - or would removal and reinstallation fix that? Curse client reports them all up to date.