It seems that many of the comments in this thread appear to focus on only one or two of the three of specifications from the OP (the 5/16" thickness & chopping presumably wood). The OP also included a third spec of only 8.5" long blade length. In general, I would assume this would disqualify many of the previously mentioned machete, kukri, and other bladed tools mentioned in support of A) 5/16" thick B) 8.5" long C) choppers.
I think the 8.5" length would disqualify a number of statements related to knives historically mentioned in this thread.
I would enjoy learning about any performers from history that really stood out as good performers meeting the OP's spec's. Most specifically, any that would NOT be made better performers by having a longer blade length. I am truly interested in learning something here, as on the surface just does not make sense from my experiences related to chopping, good weight and an effective sweet zone on the cutting edge that allows good use of a thick heavy blade.
With regard to examples batoning with an axe or hatchet; I would add to this thread that my kit includes a tomahawk and that I many times baton with it. Fine notching work is accomplished by setting the edge location and specific angle desired then batoning the back of eye, same as with a knife except that you have more options as to the angle of impact with the baton. I have also split a number of logs this way (3' - 5') to make bench seats (half logs resting on notched rounds, etc.). Many other uses for batoning with a hawk that I would suspect also would translate to a small axe or hatchet & batoning. I prefer the hawk (to say a hatchet or small axe when packing in on foot) as the bit is easily removable from the haft (and is a very useful tool by itself and/or with a batton, think wood chisel, ulu, etc.). Had a epic day by the river batoning with a hawk & site-made wood wedges splitting off planks of wood from an old growth cedar that had been taken down by river flows along a undercut bend. Hope this helps illustrate, for those in question related to the merits of this application.
Batoning pic added:
This piece of cedar is part of one of the smaller sections reclaimed/harvested in description above.
In this example, I was attempting to establish how narrow a V was required (for depth of cut) to make it through (waste reduction/conservation).
The narrower the V, the more the cut comes closer to a true crosscut (more difficult, but less wasteful of this sweet old growth Western Red Cedar).
The dents & dings on this hawks haft are from throwing, NOT from overstrikes batoning. Throwing hawks creates forces that can dislodge the head from haft upon impact with target while at the same time the inside of the eye makes these nasty depressions as the haft fiercly rattles is way loose in the haft. "Character marks" v. marks of carelessness are worn proud

Sections were then planked out into fire-boards & spindles for fire-starting projects (again batoning with the hawk). I see DeadBoxHero already posted a nice pic illustrating batoning with the grain of the wood in a firewood splitting application.
Splitting & Planing (included batoning):
Bench, supports, & a shelf (left foreground) used batoning in various applications to accomplish.
EDIT: I just re-read the OP and realised it stated 8" - 12" blade length (I mistakenly read this as 8-1/2"). My bad sorry, 10" - 12" range is much more understandable. However, I would still believe that weight distributed across a higher blade profile would perform better than going the super thick / short-blade-height route. Similar to the performance benefit a pole adds to an axe, tomahawk, etc. (increases the swing dynamics & energy transfer to the edge upon impact). Still interested to see any historic performers that meet the OP.