Radeon 4850 ~ GeForce 9800 GTX
Radeon 4870 ~ GeForce GTX 260
But this doesn't mean that they produce almost the same fps in games. In some games, the Radions excel, in others, the Geforces do (and they excel quite a bit), and the Radeon 4870 struggles with resolutions higher than 1600x1200 (probably due to a lack of video memory) and cannot compete with the GTX 260.
By the way, NVIDIA's pricing policy also makes you think, because it's not for nothing that they started lowering prices on their chips a few days after the release. I suggest you take a look here. I based my message yesterday on this information.
P.S. I don't know about you, but I'm tired of NVIDIA's constant leadership. Not only is it simply uninteresting to read tests where the "green" cards are predictably in the lead, but they also inflate prices, albeit within reasonable limits. Now, for the first time in a long time, NVIDIA is facing fierce competition, everything will fall into place, and the average prices for top-end products will automatically decrease. We should be happy about this, not sad about the failures of NVIDIA, which some people love.
Bow down and hear our cry,
Our earthly rulers falter,
Our people drift and die,
The walls of gold entomb us,
The swords of scorn divide,
Take not thy thunder from us,
Take away our pride.
G.K. Chesterton: English Hymnal