I get with my 908, 922hp, pre installed setup, with both engine and rigidity in bad shape, the following times: 30,5 to 31,1 sec at Like The Wind
My 787b Mazda Stealth, pre installed setup, with 927hp and great engine and rigidity (it just costs 500 cr every time) I get 30.9 to 31.5 sec.
So I guess the 908 is better, heavier, yes, but with better aerodynamics and suspension.
As a diesel engine, the 908 should be also better for the endurance races aswell.
But the Mazda feels much more stable at high speed, over- and understeer are exactly at the perfect middle on the Indy high speed track. The 908 always feels a little too optimistic, you can easily loose some 00.X with oversteer at the end of the long corners and when getting her back in a strate line. Also it's harder for me to directly hit that one perfect hot spot of every corner. So in fact it's easier to get a 30.9 almost always with a Mazda then a 30.5 with the 908.
edit: need to back check my times. 30 sec not currect. I think it was 40 sec.