Here are a few tips:
FSX is BIG == 14 Gb just installed. It's a HUGE number of files.
The very first advise would be to install it on a separate hard disk, or at least a separate partition. Defragmenting the disk where FSX is installed is very important for the loading speed and the general performance, so installing FSX on a dedicated harddrive or partition will ease and speed up the defragmentation.
Then, just follow the installation steps: FSX, then SP1, then SP2, and then only you begin to apply the tweaks. You've spotted the topic with the explanations from NickN already, so you know what to do/test.
