According to NordicHardware, AMD will roll out a 40nm RV740 core in Q1 2009 and the site also suggests we can expect a new high-end GPU in the same timeframe.
The first new high-end 40nm GPU from ATI will be the RV870 but we still know very little about this chip. Unreliable sources claim ATI is aiming to put 2000 shader processors in this chip but we don't know if this is feasible.