Where did you read on this forum that in order to score above 900 you need to solve ALL problems from Irodov's book?
The real PGRE problems are simpler than the majority of problems in this book. Furthermore, solving ALL of the problems from one book that was not written specifically for the PGRE preparation is a waste of time. Instead of this, take a look at officially released tests and by solving them identify your weaknesses. Then you will be able to choose
what problems you actually need to solve in order to improve your score on the real test.