Not sure if this helps, but I did some back to backs already
A nice twisty track
http://stracker.simracing.org.uk:50041/lapstat?track=sebring&cars=bmw_m3_gt2,ks_corvette_c7r,ferrari_458_gt2,ks_porsche_911_rsr_2017&valid=1,2&date_from=&date_to=Porsche time is a little misleading because I messed up the 1st sector on that best lap and there is another 0.3 in there, 458 and Vette were on it!
Strangely at Spa the gaps were closer, I did try Porsche but had to do it offline as the server was reset to another track, but with same track temps/grip it was possible to do a lap in the low 16s
http://stracker.simracing.org.uk:50041/lapstat?track=spa&cars=bmw_m3_gt2,ks_corvette_c7r,ferrari_458_gt2,ks_porsche_911_rsr_2017&valid=1,2&date_from=&date_to=From the test race a while back at Interlagos the BMW was close to the Ferrari for me, with the other 2 faster...
Road America might give a decent set of results - some long straights, and a mix of fast / med / slow turns
Edit: not sure its really possible to blunt the porsches top speed advantage though, adding weight will only kill the accel a bit, top speed will still be higher so for Le Mans LOL