To fire 40 rounds the Lee-Enfield would require 6 clips and the Garand 5
Only if the Lee-Enfield starts with a full magazine and the Garand starts empty. If the Garand starts loaded (8 rounds) it only needs 4 reloads to get to 40 rounds.
Both stripper clips and enbloc clips tend to vary in Spring tension and actual size. Most Competition shooters had favorites or selected stripper clips, enboc clips and detachable magazines depending on rifle and had them marked as to ownership and in some cases, order in which they were to be used.
Hammering bolts closed or open when the bolt guns get dirty only works so long and certainly slows the rate of fire. Better than using the rifle as a club though.
Trying to clean the locking lug recesses on a Springfield or Mauser isn't much (if any) easier than cleaning them on an M-1.
Locking lug recesses are well inside the forward receiver ring.
I have no idea how objective the Marine corp test was. US rifle tests in the 1950s for the M-14 vs FN FAL and M-14 vs AR-15 were not only biased they were sometimes rigged. ( guns dismantled and reassembled using improper tools and using improper tolerances).
The SMLE had no hidden locking lug recesses and could be cleared much easier. The British guns also had over sized chambers which would hold a fair amount of crud without the need for hammering on the bolt.
Hammering bolts closed on dirty/gritty ammunition or chambers could very well result in a stuck case once the the gun was fired and while the bolt guns
might tolerate bolt handles being beat on with rocks or boot heels better than the semi-autos there was a fair chance on either type of gun of pulling the extractor through the rim leaving the case stuck in the chamber. At which point unless you have several minutes to work on the gun uninterrupted with the proper tools it is pretty much a club no matter what type of action it has.
Hint, it is even possible to bend cleaning rods without removing stuck case.