I too am in the process of building a long-action 700 custom rig. While researching the right stock for the build I was fortunate enough to handle both the Fully adjustable McMillan A-5 and the Fully adjustable HS Precision side by side and found that the HS Precision was not only $100.00 cheaper for the same options and much lighter but the workmanship seemed better than that of the McMillan stock. For me there was no comparison, however this is my personal preference. I chose the HS Precision PST-26 Pro series fully adjustable stock and will receive it in only six weeks vs. the 3 to 4 months McMillan is quoting for a lead time.
Remember McMillan make their stocks to order and to the customer specification. So one A5 doesn’t represent all A5's. Weight, finish, color, etc are up to the customer.
I would go with the A3 or A5.