A long while back there was a thread and down in a ways it was stated that a large tool manufacturer stated that it was always best to pick a tool with a shank diameter the same or as close to the cut diameter as possible. So a 1/2" cutter, 1/2" shank, 1/4" cutter 1/4" shank, etc..
We cut miles of 1/4" MDF and have always run 1/4" or 7/32" 2 flute straight plunge with 1/2" shank. Typically run 22000 at 500IPM and the tools last, well, pretty much forever as I have never tallied how many sheets on a tool but I have cut several hundred sheets on 3 - 4 tools a couple of which I still keep for backup/spares but depending on the material that lands they are dull enough to leave a tiny fuzzy edge and the parts need to come off the machine dead clean with no handwork at all.
So last tooling order that comment popped into my head and I tossed 4 Amana 1/4" shank x 1/4" dia x 1/2" CL tools on the order. At $13+ a piece I though why not.
First bit didnt make it 2/3 through a sheet and snapped. Second bit, cut the feed to 350ipm ran the remaining 1/3 and the second and snapped right at the end. A used 1/2" shank, 1/4" diameter 2 flute plunge went back in the holder and ran the five remaining sheets for the job. The two new bits will be relegated to fragile little bird type work.
Its plainly clear that the large fillet at the top of the 1/4" tool to the 1/2" shank adds a massive amount of strength and rigidity to the tool. It eliminates any stress risers at the top of the brazed portion of the bit, and also due to its mass will carry off way more heat.
I knew it was just common sense because even with hand routers performance is always improved with 1/2" shank tooling but its always great to do some real world testing even if it costs you 30 bucks and a bit of time re-toolpathing.
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