performance benchmark for pre 66 FIA cars

[simon drabble]

this is really an evolvement from Terry's excellant thread on what car you would like. I have assumed only cars eligible (and likely to finish) the 6 Hour at Spa as this is a destination race for many....
what I am interested in is the expected optimum time for a legal car and then try and assess relative value. For example a legal MGB can probably do Spa in 3.12? a Mustang 3.07? a 911 in 3.08? I would be really interested in people's view as I would be fascinated in the value against performance as that can then illustrate the "underpriced" cars or perhaps that should be less overpriced!
My guess is that MGB's, Griffiths, Ti Super's will come out well in this but I am interested to see what else does...