Finally, I tried iRacing. Thought that, compared to other games, 20 Dollars for one month of gameplay is actually quite a good value, most games cost more than twice for half a day.
Now here's my verdict:
For me, iRacing feels like a mixture of LfS and the Simbin-Sims. Now that could be a good thing, but it isn't, because to me, it has the weak points of both, with not much things that it does better than any of the two fomer.
The driving physics, often described as superior in here, don't cut it for me. Now I've only driven the Solstice, as I haven't bought a single seater, but it drives very much like a non racing tin top in GTR-Evo: lot's of tyre squeal on almost every steering or breaking input, which makes finding the limit very hard, and it feels slippy and somehow detached from the road. Force Feedback is despite a resitance to turn the wheel, almost nonexistant, which doesn't help either.
Soundwise, it's also right between LfS and Simbin: it does sound nice, but the sounds are canned, much like Evo, but it lacks the spectrum. All you got is engine, gearwhine, wind and tyre squeal, much like LfS, but without the depth of information you get out of it.
The damage system almost looks exactly like LfS, allthough your tyres and suspension are very easily pushed away from their original positions, which, somehow doesn't affect the driving much, at least with the solstice.
The graphics look good, bit for some reason, even without limiter, i'm stuck at 30-40 fps when alone and 20 fps when more than two cars are visible, which makes racing quite a gamble in the first few corners. I can't find the graphic setting that would solve this problem.
Now I also don't think that iRacing is a LfS Killer. It wouldn't even be, if it did perfectly, for one single reason: because of it's pricing and system, it's aimed at experienced racers, it's definately no game somebody who isn't into sim racing would buy. So to me, it's rather a follow up for current simulations than a competitor, for people who long for the quite elaborated system behind iRacing and are not satisfied with what common on-line racing and leagues have to offer, rather than simply looking for better physics.
Personal Conclusion: SOme nice ideas, at the moment, I'd still rather stick to live for speed.