Well, it should not be too far off in any case, but I agree the since 6h of SPA was the first race the R18 '11 participated in, it can only get better
By comparison the times for 2012 and 2013 are the following.
Race facts Spa 6h 2012:
-Audi R18 Ultra fastest Quali lap: 2:02,093
-Audi R18 Ultra fastest lap in race: 2:02.437
-Audi R18 E-Tron Q fastest lap in race: 2:01.851
Race facts Spa 6h 2013:
-Audi R18 E-Tron Q (Long Tail) fastest Quali lap: 1:58.934
-Audi R18 E-Tron Q fastest Quali lap: 1:59.336
-Audi R18 E-Tron Q fastest lap in race: 2:02.083
So lap time has decreased by a couple of sec the last years.
In any case when the R18 '11 was modeled in GT6 I think we can agree that is should be performing in the 2:03.XXX - 2:04.XXX without SRF with RH tires.