There are things that McMillan will offer that no one else out there currently is offering, if these options are what a person wants there is a price to pay. If you want the most popular tactical style stock used right now, the A-5, again you will pay in waiting.
There are other options if you want a similiar stock as mentioned, Joels stocks are great to work with. Just bedded one up for a customer in 338 Allen Magnum. Will be an amazing rifle and his service is top notch all the way.
Manner stocks are also great options as are HS in certain applications.
Your referral to Shawn probably has as much to do with the guy that built the rifle and is shooting the rifle as opposed to what stock is on the rifle. I have shot with Shawn and shot his rifles, he is also a world class smith.
As to if the stock makes that much difference, again, I have built rifles using factory Laminates wood stocks. Two specific rifles come to mind, they were my personal 270 Allen Magnum based on a Savage M111 receiver with factory sporter stock and the other was my 7mm Allen Magnum based on a Rem 700 with a factory Laminate Sendero stock.
Both rifles were extremely accurate, both rifles took big game well over 700 yards and both rifles killed rock chucks with one shot kills over 1100 yards. Both rifles were also tested at over 2000 yards for accuracy and both held well under moa even at that extreme range. And this was with $100 stocks.
Again, it is my opinion that if the bedding is stress free and the rest of the rifle is build properly it WILL be a shooter, even at extreme range.
Still, if you want a McMillan A-5, you will have to order it from McMillan and get it when you get it. I guess thats all there is to it. If your happy with another quality stock, by all means order from a different company.
It is becoming well known that the A-5 takes a long time to get in. I tell this to every one of my customers that order custom rifles
from me. Funny thing, I order A-5s at a rate of 5 to 1 of all other stocks combined and that is after I tell my customers about the long wait. Must be something to them as the orders just keep coming in.