Interesting debate regarding op rods sizes, style, spring make and size from some knowledgeable people here. I suggest that all your theories and personal tests are a good resource but really should be independently tested.
So, I am will to conduct independent tests to confirm your theories regarding accuracy improvement (or not) by changing op rods and springs. To facilitate this independent testing, I am asking you to send me the different makes and styles of op rods and springs. Also send different M14 platforms (rifle in mystery wood, rifle in a GI stock, rifle in a plastic stock, etc). Also send a sufficient supply of ammunition to break in, test fire, warm up, set up, practice each M14 rifle prior to the start of the independent testing.
I realize that this offer will place a burden on me, taking me away from my family, but this is a sacrifice I am willing to make. Send me a PM and I will provide you with an address where you can send everything.
If you have an open mind, not adverse to manual labour (loading mags) or frequent repetitive motion and actions (shooting and shooting), I may be interested in assistance in this daunting task.