DDR2 speed

Hi all, I have a pair of tow Corsair modules each on with a capacitie of
2048 runing at 1066 at CL5-5-5-15 dual chanel interleave..
Now, If I run the system at a lower DDR2 frequency 837 and CL 4-4-4-14 the
system is notably faster. Are ther any problem with my Asus P5Q p45
motrheboard? Or with the Corsair modules?

Thanks in advance, Manuel

Noticeably faster by what standards?

Have you used a test that examines the memory subsystem transfer rate in
isolation? Sysoft Sandra (a free download) has such tests.

How have you set the BIOS parameters other than the memory internal timings?
Parameters like the relation between the CPU clock and the Memory clock
(synchronous or asynchronous, for example)?

What CPU (particularly the FrontSide Bus speed, but also the size of the L2
cache)?

I think the difference between system performance at DDR2-1066 / CL5-5-5-15 and DDR2-837 / CL4-4-4-14 should be very small (a few percent) IF all other parameters are the same. The DDR2-1066 / CL5-5-5-15 should be slightly faster because the delays (CL5-5-5-14 and CL4-4-4-15) are multiples of the memory cycle time and 5/1066 = 0.00469 is smaller than 4/837 = 0.00478. Also 15/1066 is smaller than 14/837, but that delay is only incurred when accessing non-sequential blocks of memory.