ATI's 65 nanometre part codenamed R650 is here to fight Nvidia next generation chip called G90. Nvidia will shrink its G90 and plans to make the same marchitecture faster and this is exactly what ATI plans to do.
At 65 nanometre ATI can go much faster and it will solve the thermal dissipation and power problems. G80 is a very strong and effective marchitecture and at higher clock will be a tough competition.
R650 as far as we know will just be faster version of R600 chip without any major marchitectural changes. Both of these chips are expected by the end of the year, sometimes in Q4 but don’t be so naïve and trust ATI on its deadline. It traditionally messed up the launch date of every chip in the last eighteen months.