The 8.8 metric class bolt is equivalent to grade 5 bolt which has a yield strength of 92 ksi. The 10.9 class bolt is equivalent to a grade 8 bolt of 130 ksi yield strength. Both are very capable. One thing to note is that when you go up in strength, you also go up in brittleness. Meaning that the bolt won't bend very far before catastrophically failing. So a typical mild grade steel bolt will bend much further than a grade 8 bolt before breaking. There are advantages to this if that is what you want.
In the case of the shock mount bolt, I think you want the strength vs bending capacity. So yes, I'd change them out. However, you could buy the higher grade hardware and keep it with you in case of failure of the currently installed hardware.
To contrast the strength vurse brittleness, think of the steering knuckles. Some think it's better that they bend first before catastrophically failing. You notice the bent part and limp home to fix it. If it breaks, you're stuck where you are till you fix it.
@
Yukon Joe
Run Raptor Run | Great Lakes Raptor Excursions (GLRE)