No, a 750-780 looks just about right for a 750+ score on Lit. (Not as right as an 800 of course,

but still very good.)
There is some sort of a correlation. The test isn't insanely hard at all really, one just has to have a decent amount of interpretive skills that's all. They're not asking you to use any sort of supernatural skills. In fact Lit is probably one of the exams that, if you're good at, you can feel very confident about as there really is nothing more that you can do to prepare for it, besides being well, who you are...
Just work a bit of the more abstruse terms you'll encounter (synecdoche and the like and hope that you'll get passages that you'll relate to)