I tried to use my IV Qbank but didn't feel like I was learning efficiently from it. However, regular Qbank wasn't all that amazing either. I know a couple of friends who actually used a good amount of IV Qbank and gave up on it after a while, and didn't really think it helped them on the exam.
As far as assessing yourself, Qbank undoubtedly is too far out there for some topics (anatomy, pharm); if you want a good question source to assess yourself, take an NBME. However, if you want something to boost your ego (which is not necessarily a bad thing), it sounds like you should continue with IV, and if you want to learn from questions I think almost any source (Qbank with a grain of salt, IV, UW, Robbins) can be very useful if you like it and use it correctly.