NVIDIA vs ATi cores measurements????

You're comparing apples with oranges.
Different chips designs have different pipeline architecture and ati's cores are hardly anything like nvidia's cores.
If you look further, you can see that despite having 3-4 times the amount of cores, ati's chips are in the same bracket when it comes to transistor count so there is no way those ati cores are even close to the same complexity as nvidia's.

Frankly, specification numbers haven't been a good way to estimate real life performance for quite a while... Nowadays, you need to understand the different needs of different applications and their respective bottlenecks to even make an educated guess of how these numbers will translate. If you're in a hurry, forgot all of those and just look up the benchmark for what you'll use it for.

Or the OP could just search the internet for one of the hundreds of other topics on it.

I would suggest looking up the 2900 reviews for better detail.

http://www.tomshardware.com/reviews/best-graphics-card,...

If you want to understand it a bit better then look at these two links
http://www.beyond3d.com/content/reviews/16
http://www.beyond3d.com/content/reviews/1/14

The new Fermi cards from nvidia are differant again but the two links while not bang upto date give a good idea of how teh differant camps Archetecture differ.

Ps just to say that there are probably some links on the home page of that site to up to date analasis of teh new ATI Cypres cores as well.
Mactronix