Both the width of the turns and the ratio of straight-away:turn ratio can vary slightly. For long sprints, wider turns are better. In fact, I just read an abstract which optimized sprint track shape and found that the ideal shape for 200m and 400m sprint performance is a perfect circle. UF’s fast, unbanked, and nearly circular indoor track is a great example of this. It’s as fast as practically any banked track in the world.
Surface also has a lot to do with how fast a track is. The harder the track the faster it is. Also the type of synthetic rubber used can be important.