When I go to my local kart track (indoor) they have a mechanic who races in British F3, I think he is usually running near the back but he knows karts well enough. When I went out on the track with him he was about 3 seconds a lap faster and lapped me like 5 times, anytime he passed me he was sliding the kart. It was a tight track with a couple of hairpins, he was sliding it on entry then just flooring it straight out of the turn. So it must depend on the track.
My first time out I was too worn out after 30 minutes to even attempt to copy his lines, it was hard enough holding onto the wheel, and I am pretty fit when it comes to running and playing tennis, badminton and football, but you really can't prepare for what a kart does to you. My arms were floppy after 20 minutes, and my ribs hurt like hell. Oh and in my opinion you need to forget almost everything you have learnt on LFS and start over.