Stoo,
We have had issues with bolts working loose and snapping on solid front mounts and also gearbox threads eventually stripping under normal torque settings, we think it is due to direct shock loading across the thread pitch which might fatigue the alloy thread eventually.
We dont have scientific evidence of this but many racing assumptions are based on our 25+ years racing car building experience and not direct science. We did helicoil the DC5 alloy threads (which we first started doing on alloy gearboxes in 1984)and this cured the problem but it is more of a "corking a leaky dam"than building a proper dam....
Also we consulted some of our dealers who have fitted both Avid and Inovative steel mounts and the story is the same irrespective of make.Thats why we opted for Alloy Billet.
Hope this helps you in your decision.