Which Graphic card should I buy

The graphic card market is so exciting that there does not seem to be an end to one's excitement.I was sure to buy a corsair vx450 power supply and if i had money,I would have gone for a gtx 460 768mb and if not then a 5770 would have been my choice.My res is just 1360x768 and i thought that any of these cards should be fine.I did not want to go for gtx 460 1gb or 6850 because they would not be utilized fully on my resolution.So when i thought that i had made a decision,i came to know about another card and i was surprised.It is the radeon 5850.I came to know that the 5850 is quite cheap these days and its performance just bashes up 460 and 6850.As i live in india , a 460 768mb would be around rs.8000 ($180).
Now the real question begins here.If i am in a situation when suppose 5850 would be $20-40 more than 460 768mb.Iwould be tempted to go for it even though it would not be fully utilized and my budget wont allow.But i would try hard and would try to get it.In such a situation,will there be any solid reason to get a 460 768 or 460 1gb or 6850 which would handle all games and not a 5850 which would be overkill but great in price/performance and would be hard to resist.?My computer is weak with c2d e7500@2.93 ghz and 2gbddr2 ram.
I dont care about 3d vision physx eyefinity better driver support or power consumption or gpu temperature.I want a solid reason.The question may seem silly but i would be thankful to those who help.