Imo Nic you should take the Zed, ...otherwise what was the point of going FI as you can't really enjoy it to its full potential on the roads (legally anyway).
All you need to do is build up the speed slowly and try not to get caught up, like some people do, with "showing off" to whomever's watching. Just have fun is the most important thing & to be safe.
I've done lots of track days/experience days over the years but below is the video of the first one I did after having my 350 supercharged.
As you can see lots of "slower" cars over take me as I move over for them etc when I see them coming up behind me. The reason for this is I wanted to build up my speed slowly, lap after lap, in order to ascertain how much grip was available to me.
Track days aren't race events so who cares if some nutter going for gold over takes you in a bashed up Clio or some other car their not bothered about wrecking.
It's just about enjoying your car safely at speed.