I wouldn't loose sleep over being slightly slower than the WR through critical corners. Remember, you never know how many times the WR holder tried before he finally got it right. He might have skidded out in that corner nine times in a row before making it on the tenth attempt for all you know.
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A better indicator would be to see what kind of average laptimes the best people on online servers have. (For example in CTRA or other "serious" servers)
In that specific corner on GP Long, "entry stability" is key. For example in cars like FZ5 you can really feel it when you're about to cross that boundary and start skidding and loosing control. (That's why I tend to stick to FZ5, XRT or even XRG when learning new tracks, because they give such excellent feedback IMO) Remember, controlled corner entry --> high exit speed. You have to attack the root of the problem.
Good luck!