My guess is that most on this board will go synthetic, but at a 5000 mile oil change interval, I'm not sure it will not matter at all. Remember, the IS-F has a 10 qt sump as well as oil coolers and a scavange pump, things that allow dino oil to protect better by itself. My guess is that more protection gains from hard/track style driving would more likely be seen from a thicker oil such as 10w-30, a high mileage 10W-30, or a 15W-40. If you really run the lexus hard, a synthetic like redline would be a good choice. For daily driving, there is no benefit from synthetic in the IS-F with a 5000 mile oil change interval.