the 9000 is NOT based on 8500 tech. the 8500, 8500le, 9100 and 9200 have the same (R200) core, more or less. the 9000 has its own core (R250), based very very heavily on the gamecube graphics chip - the upside of which is the 9000 has (more or less) a proper pixel shader and the 9100/9200 do not.
That said, R250 is not as fast in absolute terms as R200, hence an 8500 will outperform it in most applications. The 9000 was designed as a GF4MX beater, the 8500 as a GF3Ti beater
--jo