Which is better ati radeon HD 3870 or ati radeon HD 5750

Is the Radeon hd 3870 a 1GB
Check this one out ATI Radeon HD 4650 Which is 1GB has a DirectX 10.1 Support,
320 stream processing units and AGP 8x

This card works good with my Intel P4 3.20GHz But on better CPU works Perfect.