The following stability numbers come from the formula Steve Killing developed to compare different boat. The simplicity of Steve’s numbers make it easier to compare boats. Keep in mind that everyone will have a different level of comfort.
From what I have gathered reading:
110+ is comfortable for all novices
100 is comfortable for most paddlers
98 will be initially tender to some novices, but after a few paddles will be quite comfortable
92 is not comfortable to most novices.
* Contrary to this statement, I have found new paddlers are fine in my boats with a SF of 93. Typical response is it feels a bit tender at first, but they quickly adjust to it.
88 is a challenging boat for some people to paddle
40 to 50 is the low end, a K1 racing kayak would be somewhere in that range.