Anyone wishing for a car with tons of grip and probably substantially better tire wear, the Merc is the way to go, although you have to give up quite a bit of HP to get the enhanced grip. It was able to run the same lap times on GP/D as the other BMW, Opel and RX7 give or take a few tenths, not sure about the full track. It's far and away the grippiest of the bunch (stock downforce is much higher) and the easiest to drive as a result. Probably much more stable late in the run due to lower overall tire wear (more downforce = less tire wear all else the same) and probably less rear wheel spin due to the lower HP.
I've also noticed since the 2.09 update, a significant improvement in grip around the 5-7 lap distance. Not unusual to knock nearly a second off once you get to there, so keep that in mind when you see laptimes posted here.