Since you have 4 weeks left, I'd suggest giving GMAT prep at this point to get a accurate assessment. PowerPrep does inflate your score as some of its questions are also in the OG11.
It is possible to pull 40+ if you use most of your 4 weeks to focus on your weakness in your verbal (RC, SC, CR or timing issues). Go through the questions you gotten wrong in OG 11 and verbal supplement, referring to Manhattan SC. If you have timing issues, doing more CAT's certainly helps. Manhattan CATs have good verbal content with answer explanations.