Jeremy: "stack for python_d.exe has been already up'ed to 2100000"

Indeed, but not recently (changeset 97361d917d22):

<< Issue 2286: bump up the stack size of the 64-bit debug python_d.exe to 2100000. The default value of 200000 causes a stack overflow at 1965 iterations of r_object() in marshal.c, 35 iterations before the 2000 limit enforced by MAX_MARSHAL_STACK_DEPTH. >>

Oh it looks like it was the same issue: "Stack overflow exception caused by test_marshal on Windows x64". See issue #2286.

Amaury wrote in this issue (in 2008, msg63540):
"Can you try to raise the stack size on x64 builds? If 2Mb is enough for 32bit, 4Mb should be good in your case."

Jeremy: "Therefore the reserve could be as large as needed to prevent stack overflows without impacting the actually memory footprint of the executable.  Maybe we should consider increasing the reserve to match that of Linux (8MB)?"

Ah ok, if the memory footprint is unchanged, yes please increase the arbitrary limit. I would suggest 8 MB.