I have not experienced slow performance in DW CC, but I am not using Windows 8.
on my windows 7 system, and on my Mac system, I find DW CC has the same speed as CS6.
Not sure what may be causing the performance issues you are experiencing, but I Would contact Adobe Support for assistance.
The MySQLi extension we will be releasing will work separately from the native versions.
You will have the option to use the native version in order to manage old sites that still use MySQL. or use the new MySQLi version for new sites.