GT5 is going to look REALLY dated now. In my opinion Forza 3 looks much better and reacts more 'realistic' then GT5 does currently
GT5 was really "dated" the day it was released to be honest, it couldn't hold a candle to Forza 3. I mean I own both games and enjoy them both (and I definetly will be getting Forza 4, there is no doubt on that one) but unless Polyphony can pull a rabbit out of their hat* with GT6, GT is dead in the water to be honest. Don't get me wrong, GT5 is still a fantastic game but they got too ambitious (and it feels so unfinished, don't even get me started on the whole premium/standard car debarkle!) and they made the biggest mistake of doing it all in house (with such a tiny dev team), Turn 10 on the other hand has a much bigger dev team and outsourced the car models, so it's not wounder they can pump out better all round games in such a short time frame. That is my 2 cents, take with a grain of salt.
* = I expect they will, GT5 was a complete rewrite after all so most of their time was spent building the game engine, but this time [with GT6] they can spend more time polishing the engine alot more and adding in features etc to make it a better all round experience. So I'm confident Polyphony can redeem themselves.
Even though the 720 will be here, MS says the 360 still has nearly 5 more years to go. We shall see if they port a version to the 360 as well.
I hope they don't, much rather it being "Xbox 720" exclusive. I mean why would you want them to gimp it to run on the 360? much rather they took it to the next level on the 720 only, however, that is just me.