Understanding Timings & Clock

[tokyotech]

For Black Friday, Newegg has two cheap RAM:

http://www.newegg.com/Product/Product.aspx?Item=N82E16820227364&cm_sp=DailyDeal-_-20-227-364-_-Product
OCZ Fatal1ty Edition 4GB (2 x 2GB) 240-Pin DDR2 SDRAM DDR2 1066
7-7-7-20

http://www.newegg.com/Product/Product.aspx?Item=N82E16820231145&cm_sp=DailyDeal-_-20-231-145-_-Product
G.SKILL 4GB (2 x 2GB) 240-Pin DDR2 SDRAM DDR2 1000
5-5-5-15

My computer currently has:

http://www.newegg.com/Product/Product.aspx?Item=N82E16820231098
G.SKILL 2GB (2 x 1GB) 240-Pin DDR2 SDRAM DDR2 800
5-5-5-15

What will happen if I buy the G.Skill pair? It has the same timings but it has a higher clock speed. What will happen if I buy the Fatal1ty pair? Both timings and clock speed are different. Are these differences a cause for instabilities? And why does the Fatal1ty RAM have such slow timings? I thought it was a high end brand. Also, I am aware that I will need to go to a 64-bit OS to fully utilize these.

 

[daft]

if your bios work correctly, they will underclock the gskill to the 800, if not, change it yourself.

 

[tokyotech]

Will the Fatal1ty's timings be lowered to my current 5-5-5-15 or is it only possible to elongate the timings?