Windows 7: timings for ram help

Hi i have 4gb kingston 800 ram set 2x2gb.the timings in bios are 6-5-5-17 .24 clocks.
Are these good timings and can i tighten them with no damage to the ram.
I can send them back as i had 3gb at 5-4-4 .
the performance with this 4gb set seems not as good as the 3gb set ,this is on my second machine

Could probably tighten them a bit. Most likely be able to get 5-5-5-15 22. If you tighten them too much then your PC just probably won't boot up. Tightening them doesn't give that much of a noticeable increase in performance though.