Laptop memory Crucial vs Corsair and other question

Hi,

I'm hoping if you can help me with this decision. First, I'm thinking of buy either:
Crucial 4GB (2 x 2GB) 200-Pin DDR2 SO-DIMM DDR2 800 (PC2 6400)

Or

CORSAIR 4GB (2 x 2GB) 200-Pin DDR2 SO-DIMM DDR2 800 (PC2 6400)

Can someone tell me which brand is more reliable (long lasting, no errors) and faster? Maybe better memory chips?

Also, how can I check if my motherboard or chipset has a limit of 677mhz? I don't want to spend extra money purchasing 800mhz DDR2 memory if my chipset limitation is only 677mhz.

Thanks for your help!

Edit: Also I just realized that the 677 mhz memory has a CAS latency of 5 while the 800mhz memory has a CAS latency of 6. What would be better in this case?