In my experience, pulling a wheelie in a higher gear is easier to ride longer and pull up smoothly. I used to have a built 400ex and sure I could sit on the gas tank and blip the throttle and pull a wheelie in 1st. It's hard to hold it though because it's such a short gear. 3rd gear I could pull one easy and smoothly bring it to its balance point and cruise it. Once you get good at wheelies you will learn to shift while doing one. Key factor when doing wheelies, use the throttle to bring the front end up and the rear brake to keep it down. Manipulating the rear brake and throttle are key to prevent flipping over.