Hey everyone, I've been reading these forums for quite a while since I'm interested in buying the Genesis within the next year or so and came across this thread. I read an article that talked about this very topic on Autoblog this morning dated June 23 and they were pretty sure Hyundai would be putting a new bored-out 5.0 liter V8 in the Genesis Sedan and possibly into the Couple later to combat the Mustang. Though it's important to note that they did mention that there was no "official" word from Hyundai on this topic. The Equus would launch with the 4.6 and get the 5.0 when the 2011 Genesis comes out.
http://www.autoblog.com/2010/06/23/hyundai-5-0-to-take-on-mustang-with-429-horsepower/
http://www.autoblog.com/2010/06/23/hyundai-5-0-to-take-on-mustang-with-429-horsepower/