no more then 3,000 mile oil changes. this is because of the turbo. the oil is exposed to exhaust gasses more in the turbo then it is in the engine, so it will absorb more carbon deposits and fill up with gunk quicker. synthetic oil doesnt sludge like conventional oil, and carbon is a very hard material that can do lots of damage if its not cleaned out frequently. remember that most turbos will have a peak rpm of between 80,000 and 200,000, so good clean oil is essential
good info here =)
just a little bit of extra, the part of the SAE stamp that reads "SL" means that there is no zinc in the oil. modern engines dont require this additive; its mostly there for older engines that need a little extra cushion between moving parts. royal purple oil is still rated SM, which means it still has zinc. zinc is "sticky" so to speak, so it will keep the oil in place overnight and reduce damage from dry starts. thinner oil drips to the sump more freely after engine shutdown, leaving the top end starved of oil for a second or two when the engine is started until oil pressure is built up. lots of VERY good info in this thread, bookmark it, i did.