There is considerable debate about this, on this and other forums; however, much of the debate is largely borne from people's theories, lack of knowledge, too little knowledge but just enough to be dangerous, and not from fact based thinking (I include myself in these groups, of course).
IMHO, the solution is to educate yourself and read material by chemical and petroleum engineers, chemists and others deemed experts in the filed. You know you've got troubles when 2 distinct Infiniti dealers give you completely opposing views of synthetics! You'll find much less disagreement there since the information is based on known principles of petroleum engineering and engine mechanics.
I've used synthetic oil without adverse effects, and I've also owned many cars with mileage exceeding 300K-- all done with good ole dyno oil. Overall, the synthetics most highly rated are Amsoil (top of the line), German Castrol (also top of the line), Royal Purple, Pennzoil Platinum and a few others (my list is not exhaustive).
There is debate over whether some of these oils are true synthetics or not; however, for your purposes, synthetics have been used by many folks here on on other Infiniti models (I own a G35) without incident for a long time. For a less passioned discussion, you may want to read:
http://www.carcraft.com/techar....htmlh ... am...shtml
Good Luck!
Modified by W661335PF at 2:34 PM 12/10/2007