Lab results can sometimes not be entirely reflective of user experience on the site. For example if the majority of your users are visiting using 3G data rather than high speed internet, then it's likely that they're going to get a slower experience than what's indicated by Lab data. That being said, looks like your main limiter currently is your intial server response time. Your cache hit rate over the last few days has been around 60%, which is a little low, so I'd recommend increasing your default cache age to 30 days at least.