Well, it says your website is 'slow' (updated on August 10). We've had the same setup for long time without making any changes. We've CDN and caching in place so I'm not sure if I should really be looking improving it.
I thought that the Google bot is taking time because it's encountering large number of errors. I think we've relevant plugins in place and the site performs 'nice' in pagespeed tests. Am I missing out on anything obvious?
Addendum: Just did a Google PageSpeed test and got 85 (out of 100) for front page.