using external ssd as the main boot system
If I buy an iMac with a Fusion drive (which gives low performance) can I connect an external ssd to use as the main boot system to make the computer faster?
An external bus connection is slower than an internal. I doubt the minimal performance "hit" of a Fusion drive is such that an external drive would be better.
About the only thing I can imagine would be noticeable about the speed difference of a Fusion drive would be editing large video files that were stored on the HDD (until they were transferred to the SSD as they became "hot" files).