In case it helps (these are from memory so take with grain of salt) :
R2xx : Radeon 8000 to 9250
R3xx : Radeon 9500 to 9850, X300-X600
R4xx : Radeon X700 to X850
R5xx : Radeon X1300 to X1950
R6xx : Radeon HD2400 to HD3870 (there were two "waves" of R6xx, one corresponding to HD2xxx and the other to HD3xxx)
R7xx : Radeon HD4xxx
The binary drivers cover from R3xx and up, although more of the focus is on the newer chips. The open source drivers support all of the families but we don't have acceleration for R6xx/R7xx yet (it is WIP though). IGPs are always harder to map because they typically include very newest display/video logic plus smaller 3D engine from previous generation.