The performance fix is not the same as the perfmod that is included in the Streakdroid ROMs. The Streakdroid ROMs perfmod uses the internal SD card in a different way. See
this page on streakdroid.com. There is a highlighted section about the perfmod and it's use of data2ext. The performance fix does not use this.
From the OP in the performance fix thread:
This update installs custom kernel, custom build.prop and performance tweaking post_boot.sh script.
It will not erase your system, userdata or anything else. It just replaces some files.
It installs
- a different kernel (2.632.9-DJ_Steve_-BFSBFQ-OC-Vol.)
- a different boot img
- makes changes to build.prop
- Other changes
You can extract the zip file and look at everything included if you want to know exactly what it does, but it's (from my understanding) a collection of various speedup tips/hacks into a package that can be easily installed. If you want/need more details you should ask in the original thread.