I did some flying in one a few years ago and would say that the performance was virtually identical to a PA28 with the same engine.
So, if you look at a PA28-150, which is pretty well documented (or just assume 5-10% poorer performance with the same fuel consumption as a PA28-161) I think you'd be pretty much spot on.
Personally I'd be rather suspicious of claims of 800nm range. From memory the fuel capacity is 60 USgal, which is 230 litres. I used to have a Warrior that would do 28 litres/hr at about 110kn (carefully leaned, always clean aircraft, spats and teflon), at 230 litres, that would be 900nm without reserves. But, with (a) an elderly aircraft most likely without spats, (b) any tail or crosswind, (c) reserves, it's just not going to do it.
On the other hand - who in their right mind wants to fly 8 hours in a light aircraft? Make one fuel/pee stop halfway and you should have no problems unless you really are flying between two airfields 800nm apart with nothing in between.
G