How to achieve max bandwidth efficiency?

[res0n0xg]

ive got a 3000+ winchester on an av8 mobo with a gig of tccd memory. when running the memory at 2-2-2-10 at around 200mhz the efficiency from sandra is about 93-95%, yet when i have it at 256mhz its down to 82% which is a pretty big hit..... the timings are at 2.5-3-3-10. i realize the timings are slower but i just don't believe that the efficiency should go down so much.