If you are going to run Redline go ahead and stick with the recommended schedule. I would sample at 5000 miles and see how it is doing. If it is ok you could slowly increase the interval. If you are going to use anythng else includeing Mobile 1, Amsoil, or even dino oil I would not let them go past 3000 miles. I have not owned a Toyota sludge monster but I belive that 3000 miles is about all most oils will take in these engines. The only exception is Redline and that has been reported by a couple of different sources. The most respected source to report good results with redline in Toyota sludge monsters is Terry. If you type in 3.0L Redline Test you can read Terry's post about a 3.0 Avalon.
Has anyone explored the idea of single weight oil in warmer months in these engines? I am also woundering about 15W50's ........ The reason I ask is that when I was working on these pre-1997 Toyota engines almost all of my clients used 20W50 conventional and 3000 mile oil changes or they used synthetic 15W50. None of them ever practiced extended drains and I can not recall any of them ever haveing sludge issues. The few engines that were sludged were not regulars.