Suggestion:
This is my opinion only, and others' will differ:
You're doing yourself a disservice by booting the Mini from an SSD in a firewire800 enclosure. The enclosure can't support the speed of the drive.
Try a USB3 enclosure, or a USB3/SATA docking station BEFORE you open up the Mini.
I promise you that you will be AMAZED at the speed difference.
Be aware that "doing the internal surgery" on the Mini presents various opportunities to break small connections inside. Just another posting up this morning from someone who tried to do the job -- and BROKE the IR connection on the motherboard. So be sure that you go into this fully aware of the pitfalls.
Also be aware that there are almost no advantages to booting and running internally vis-a-vis doing so externally.
The two things you CAN'T do when booting externally:
- enable TRIM (unless it's a thunderbolt connection)
- do some firmware updates
Having written that, I've been booting and running my own Mini externally for almost two years, with no TRIM-related slowdowns that I can perceive. I've had a Crucial m500 as my external booter since March, and the read/write speeds (tested using BlackMagic) are virtually the same now as they were the day it was installed (without TRIM).
One of the fastest external USB3 enclosures:
http://firmtek.stores.yahoo.net/dlite1.html