I have been trying to watch this development close. What ATi is bringing to the table seems to be new. They really seem to have figured out what they need to do to get their cards to give Nvidia a run for their money. Maybe they bought an 8800 GTX or whatever and realized what works and doesn't, but from the video I saw of the HD4870, its rendering is far superior to the 8800 or 9800 line of card from Nvidia.
I did see the Nvida rendering video and had to say... I was disappointed. It looked very cartoony and just a little clearer than the 8800 line.
ATi rendered an entire city which looks photo realistic and also did a robot, dog, war machine, thing and have to say that I had a real hard time figuring out if it was real or not. The color was spot on, light reflection was perfect, impurity of the models structure realistically effected light (like uneven paint or damaged paint). To see that level of detail was astonishing.
If I had to compare the two videos to tell you how the cards would do, ATi would beat the snot out of Nvidia. But as we all know, Nvida laces their cards with crap and speed and just make damn good cards.
I am really hopping ATI pulls this one off because I want to switch to the 4870 from my sluggish BFG 8800 GTX OC2.