Perhaps. But in the world of extreme duty fasteners, it most certainly does. I used to repair shall we say, government things, and we found that we had to go a grade higher. However, our bolts were critical enough that they came individually wrapped, with a cardboard sleeve over the threads, in a sealed plastic back. $485.00 each in 1981. Each. But they were very very good bolts. Complete with label containing lot and serial number inside that bag, traceable to the mine the ores came from. So we're probably talking a different order of magnitude here.
However, with today's global sourcing of parts, the days when you could be assured that the grade 5/8.8/etc bolt you have in your hand met the grade they claim it to be is somewhat dubious. It is probably an 80% chance or greater it will be fine, but in a critical place, I'd go to Yamaha and buy it from them. You have to believe that they take their sourcing seriously and at least attempt to filter out the slag filled examples that somehow make their way into consumers bolt bins. So the quick confidence builder is to go up one grade and hope for the best. That's what I was trying to state. Personally, after being in the business for as long as I have, I've never had a problem with too high a grade, but have with too low. Some of the items in my current position require 780-900 ft/lb torque specs. Try that with your Craftsman torque wrench!
If it were a suspension fastener, or any similar load/criticality part, the factory bolt or one from an absolute trusted source would be my only choice. Bolts to mount GPS and iPhones can be brass, for all that matters.
As for brittle fractures: it usually happens with lost motion; so much slop it is hammered and hammered into submission. Softer bolts tend to deform under such loads, and this may not be readily noticeable. Also, stainless, with its high content of nickel and chrome, tends to be somewhat less strong, although there are very strong grades of stainless. The common ones are tough, but not strong. Krieger rifle barrels of Wisconsin, makers of word class rifle barrels, states on their website that they do not recommend stainless for very cold climates, and require a substantial diameter increase when going from their 4145RS CM barrel material to the stainless 416R material. Perhaps they are being extra cautious, but with their track record, I would tend to agree with them and take their word for it.
Sorry for the book, it tends to be how I write.
