Depending on how long your ‘long run’ is and what your stomach is comfortable with, I would probably still eat a breakfast and then if I find that I don’t feel good until 30+ min into the run because that breakfast hasn’t hit my system, then I would consider using a gel. I would probably still eat the breakfast but then just take the gel soon before heading out the door. My theory being that the gel will help to spike your blood sugar at the start but the food in your stomach will slightly blunt the spike and smooth it out for the rest of your run.