Actually, the Infiniti EX will be the little brother to the FX. Expect the EX to be more in line to compete with the X3.
The FX has been on the market for 3 or 4 years now, and it was really the first crossover in this vein. So one would more accurately say that the X6 is BMW's FX.
Given the heat the X6 will put on the competition, there is no surprise that Infiniti plans to update the FX soon. Rumor has it that the V8 will go to a 5.0 liter approaching 400Hp normally aspirated. So I'm really hoping that the turbo charged 4.4 rumored for the X6 comes to be.
Here's a link to the release on the 2009 FX50:
http://www.topspeed.com/cars/infinit...0-ar40452.html