You're VFR. You see another plane converging on your path at the same altitude. You have him on ADSB. You have him visually. It appears you are faster than him. You continue and, according to ADBS data, you come within one mile of each other with the other plane passing behind you. Had this happen yesterday. Based on data available to me he would pass behind me and he did. Thought about descending for separation but didn't. Maybe I should have. I was heading 010 and he was probably 050. Was 1 mile too close? I was talking to ATC, he wasn't. ATC was fine, as they should be, as long as I had visual. They did ask a couple times though. We fly 1000 feet (way less than a mile) vertical separation all the time, but the vertical vector has less speed than the horizontal. Maybe I should have descended.