from what i have heard and experienced, q-bank has a pretty weak correlation for scores to step 1. in my experience, i was getting around a 65% average, and i scored a 192/78. most folks i know in the 60's passed, and in the 70's killed it.
the NBME self assesment seems to have a much better correlation, but it is not accurate. again, in my experience, i got a 470 on the self assesment (just below the mean) and my real score was about 1SD below the mean. but, that is by far the worst result i have heard of. most people do better on the usmle than the self assesement, and i may be the only person that actually did worse.
correlations are tough. do as many questions as you can, and really understand what is right and wrong with each one. if you are in the 60's on q-bank regularly toward the end, you should pass. if you want a correlation, take the self assessment, but don't let that give you a false sense of security (just remember my sad story🙁 ).
good luck