It will cause an increase in performance. Anything under the rated timings will always 3-3-3-9 would be even better yet, or 4-4-4-4. My OC-Z Platinum sticks did either 3-3-3-8 @ 400 mhz or 4-4-4-4 @ 500 mhz. They were PC2-8000 rated 4-5-4-15 though, maybe same ram. Voltage was 2.25