the first thing i've noticed is that you've got 4 different caching/optimising plugins on there and my guess would be that they're all pulling at the same resources and working against each other. pick one, and ditch the others (WP Super Cache is usually fine for most applications of wordpress)
the other issue might be the theme, have you tried switching back to the default wordpress theme to see if things speed up? if that makes a difference then you'll need to go back to the theme's developer and ask for help as it's a commercial theme.