Geforce DDR and Geforce 2 GTS are surprisingly similar. Especially since you had your Geforce DDR overclocked... The Geforce is memory bandwidth limited. The 120 mhz Processor on the Geforce 1 and the 200 Mhz processor on the Geforce 2 barely change anything. It all has to do with your RAM.
Since the Asus was overclocked, it was able to preform almost as well as your GTS.