You could solve this all by looking and seeing if there are any recorded times yet. Also the 918 wont ever be in GT as long as a certain company allows a certain gaming company to own rights. The other two are a matter of time I'd say.
Either way as was said, comparing spec built cars to unlimited hyper cars that cost way more than a NASCAR or V8 Supercar is redundant. If you want to compare then ask the question over again with in regards to hill climbing, F1, P1 LMS cars that sort of thing where the field is equal.