My "definition" of excessively gusty is when it is not fun to ride.
From my experience, this is when the the range of winds during riding commmonly double from lull to top end.

Examples... 10 to 20, 15 to 30, and 20 to 40. I have also ridden in 30 to 50.

By defintion, in these situations, the power you experience varies by a magnitude of 4 fold while riding. That makes for unusual riding, especially if you don't even sheet out the C-loop like myself (I know... weird)

I make this more manageable/fun by rigging the kite for the gusts and riding a large board to keep me afloat in the lulls. So on a day where it is 15 to 30 (alot, not just occassional puffs) I would rig an 10m kite and use my Underground 157. In the lulls I am riding underpowered but not losing ground, in the gusts I am holding on, and in the middle, I am quite happy.

Obviously the bow kites makes these days ALOT more manageable.
St. Pete, IMO, is a gusty place, so my 157 is my go to board.
Every one approaches riding different, so my way aint the "right way", but that's how I do it, Rick, I rig for the gusts and ride a slightly bigger board than the average guy. On a steady day, I rig bigger than most people.

The day Tom got dragged, I called Eagle's phone 10 minutes prior to the incident leaving him a message to please beware and tell others because doppler looked like HELL and it was obvious something was up. (Remember Brian?)
Immediately upon getting my message he called me back (that was about 10 minutes after Tom got whacked) We were ALL upset and concerned for Tom.

I spoke with Tom for at least an hour that day, letting him vent his angers (which is usually the result of fear) on me, instead of his girl. (I recommend you don't vent about getting whacked to your girl, she might ask you to stop kiting). I have been worked several times, so I knew he was scared/pissed and needed to talk. If you are not scared of wind events (especially after getting worked), you really should be.

After talking to Tom at length, it became clear his QR failed after multiple attempts at pulling it. This was discussed at length on our local forum.
In the final analysis, it was discovered that the QR allowed one to rig it backwards and that this may have been what happened. Tom is a very safety oriented rider,especially coming from a cave diving background. The QR failed several times that day.
I have a QR on my C-loop and a shackle (as backup).
My QR failed once, luckily the shackle worked. These events usually happen within seconds (or less). The further from shore you are when it happens, the better.