Are you wanting to add this stick to your current setup or replace your 2x256 with the Hynix. If you are wanting to replace, then this Hynix would crank on up to PC4000 speeds, although it is 5 ns (DDR400) rated ram, it overclocks real well at relaxed timings therefore it has been USED in PC4000 ram, just like DDR333 (PC2700) Winbond bh-6 which was speed binned to run 200 was often used in PC3200 modules (Mushkin PC3200 2-2-2 Special, for example). It will not run well WITH your Winbond ram so if you are wanting to add vs replace, i would not suggest it.