>> I've done a 2:49.917 in the Porsche 911 RSR at Spa. ALso a 2:53.546 in
>> the Porsche 914. Both times were quicky laps simply to advance thru the
>> career mode. I would imagine with some setup editing and time dedicated
>> to the track, improvements would be likely. I don't have the 906 yet,
>> so I can't offer a time for that.

I took a look at http://gtl.gplrank.info/ , the 911 RSR may be the fastest.
Fast times at Spa are in the low 2:40's, 911 RSR, Pantera, BMW CSL, Capri RS,
Escort RS, 906, Corvette. The AC Cobra and 914-6 are a few secs behind.