Driver input as has been said will have a huge effect on laptimes.
At the Goodwood Revival I've seen originals putting in times of around 1min 24s per lap and that is quick!. It used to be said that as a novice, getting below 1 min 40s was a target for what were basically road GT40s (mainly GTDs) although with a little additional setup and improvement in setup, getting below 95s would be quick now.
I should add that at the Revival they are running on period rubber, with period brakes etc, although they are often very light. eg sub 900kg.
My own fastest lap there is just under 90s as a flying lap and just over as a standing start (that was scary!:shocked2: ) - both in Roy Smart's GTD40.
Now, to put them in perspective, I'm not sure what Martin Weigold's fastest lap at Goodwood is, I'd suspect it's about the same as me, but when Mike Wildes (Professional driver) jumped into '6 GTD' for a few laps, with Martin as a passenger, within a couple of laps he was SUB 90s!! (86s I think) and Martin came in with eyes like saucers and was amazed at what Mike could achieve in a car he was driving for the first time and in what seemed a very relaxed manner in the cockpit.
So, with modern brakes, engines, tyres etc, I'd expect a rep to be quicker in the right hands. Unfortunately the right-hands are not mine, seems the older I get, the quicker I was, (or should that read the older I get the 'braver' I was) although I may test that next year when I try a bit of circuit racing too.
Anyway, whatever you decide, putting it on track and pushing yourself and the car will give you an immense amount of pleasure and those spectating will love it too... enjoy! :thumbsup: