My experience with hot (max, over max or otherwise) loads is that you will see shorter brass life (loose primer pockets, case head separation, split necks etc) sometimes case life is drastically shorter 2x fired = trash.
Is it worth it for miniscule gains especially in something like a 6.5 grendel ? Probably not.
As STC has illuded too there are many other factors to consider when deciding if a load is too hot, but what I can suggest is that all other factors unknown velocity is a very good indicator of pressure. If it's over book max in velocity for a given projectile and powder combination then it's almost certainly over pressure. As per previous comments at best you'll shorten your brass life, but depending how over pressure you may be playing with fire.
Even loads that are below book max in charge weight can be over pressure depending on othe variables such as seating depth, brass capacity, chamber length, etc so don't assume that cause it's only just over book max that it's probably safe.
Chrono it that will tell you alot, or pull the lot and do your own load development.
I know some people believe chrono are the devil but they can also tell you a lot about where your at if you use them properly and not just to chase the highest possible velocity.
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