Garret, I understand what you're asking and appreciate the Q&A on our forum. I have been busy lately answering noob questions over on Facebook where many of you all are spending too much time!
Several years ago, Jack Melton told me that nice Mac Mason lettering increased the value of shells 2-3x. At the time I thought that was low on the high end, but turns out he was pretty right. Back then there were 4 main people running up Mac stuff, but now there aren't as many.
Of course, the math is different for an inexpensive item such as a bullet where a $5 bullet is worth $35+ if the lettering is terrific.
Gary, it happens that I have 17 Mac marked artillery projectiles. Slemmer asked me yesterday when he was negotiating to possibly buy something from the Plumber based on his trolling comment above. I have never paid anywhere near what Dickey's consignor is seeking. I paid the most for the 4" Read shown on page 111 of McKee and Mason, but that's because its a rare shell. I probably paid 1x value for it, but it was still well over $1k. I also paid over $1k for a Ketchum grenade with fins that Mac had marked, but that's what they go for even without his writing.
Besides that, I haven't paid outside the range that Jack told me years ago and I have been fortunate to come in under that multiplier more times than not.
So, I think G-man is right on the base (eg unmarked) value of this shell. Multiply it by 2 or 3 and you derive a value of $900-1100. It is a nice one. Dicky if you are watching, tell your consignor I'd pay that!
PS: I have had good dealings with Dicky and agree he is a stand up guy. My only beef with him is he doesn't have enough artillery to sell! But when he does it is usually nice. I drooled all over my keyboard about his relic pyramid he recently had for sale.