I would do it as long as it's on a Friday/Saturday.
Would prefer something a bit slower than the GT pro's, I wouldn't expect to last long with them....
How about the R8's or something of a similar speed?
rFactor it is then. Which means less numbers.
Before you all get too excited: the game only supports max 120 minute races
If it helps any planning, we recently ran an Inter Club Challenge at Spa 2004 in GTP cars, and the top drivers completed 50 laps in 2 hours, including 2 parade laps before a rolling start.
BTW, I'd highly recommend the manual parade lap start for such a long enduro, in case a few drivers end their race at Eau Rouge in the opening lap.