No man, u still can't use it as "roughly" comparision for real world performance in games as its only one of the factors from how a card performs. And "based on the information we have" is a graph that shows performance in bars. One bar is this high, and the othe bar is 4 times higher, why would nvidia make the bar 4 times as high if it was less than double the performance? Then they would make the bar 80% higher aka 4/5th times higher.
Why would they make the bar four times as high when it's only 80% faster? Because it makes their product look faster and better, it's as simple as that. That's what companies do, day in day out. If the GTX280 really was 4x faster, we would know about it for sure and nVidia would make it perfectly clear on that graph. I've shown you two independent sources - the graph and the specifications of the Ultra and the GTX - to back up my theory. What backing do you have for yours?