Niklas,
bigtop is good for general monitoring, but it's not good for highly detailed data. If you watch the timestamp in bigtop you'll notice that not every query is at exactly 2 sec. Using longer update intervals corrects for that, but then you're back to 10-second resolution. bigtop is great for getting an immediate idea of what the general traffic level is for your vips and for the system as a whole, but
You may want to take a look at the output from the tmctl command. It's more of an internal tool, and the format of the output and syntax both reflect that, but it would be easier to get the data you are after using tmctl than using parsing bigtop output. tmctl will also let you retrieve far more data than bigtop will.
--jesse