What was your vertical speed? What was the G-load on the airframe?
Overstressing the airframe is not (just) a factor of IAS, but also of G-load, vertical speed, wind (turbulence especially), etc.
Try it again under controlled conditions and see where the limits are. Then consider whether those are realistic or not.
Then try the same with the default aircraft and see if it is something specific to the model or generic.
Or just turn off the overstress damage option and have a ball