Looking at some new RAM.

Solution
Not at all, if you can get that RAM for cheaper go right ahead!

Worse case would be that it clocked itself down a bit, but that wouldn't hinder your system at all, you just might not be getting the full speed.
1) Yes, that RAM should work on the P8Z77-LX

2) The frequency of mudule to get really depends on the CPU you have. If you have an unlocked 'k' processor with a mild to moderate overclock your system could benefit from the faster 2400Mhz RAM. If you have a locked processer stick with the 1600Mhz.