Well, here we go. A picture of the Abrams next to a guardsman doesn't look too bad.
But then, when you see a picture like this, showing the real tank and some crewmen next to it, my model looks a bit too small, and the guardsman too big.
So let's put it side by side with a Leman Russ.
First thought: Holy crap! Leman Russes are HUGE! Second thought: That Abrams is way too small. The guardsman just looks too big next to it, and the guardsman's base just makes it worse.
So a 1/57 scale Abrams just isn't going to stand up to a Leman Russ. Let's delve into this a little further and see what scale might work better.
Here's a picture of an M1 Abrams, with the commander and loader standing up in their hatches.
Here are the two images side by side for comparison:
So I decided I need to rethink this. Warhammer 40,000 miniatures are a "heroic" scale, so I think my M1 Abrams needs to be "heroic" in scale as well!
The second time around, I decided to start with parts that are used for the Leman Russ and other vehicles, and scale the M1 around them. A perfect starting point is the crew hatch, since it's a standard size across 40k vehicles.
Here are two hatches from the Leman Russ kit, placed side by side on my Abrams model.
Here's a crude photoshopping of my crewman with the Abrams photo, upscaled to match the hatches. We've jumped from 1/57 scale to 1/42 scale. Now the crewmen, if anything look a little too small. But on the other hand, the Abrams looks very large, and definitely fits the bill of the "heroic" scale of 40k vehicles.
I think each scale possibility has its tradeoffs. But I think 1/42 is the way to go. The tank will be huge, but it's supposed to be huge. Also, at 1/42 scale, the track wheels of the Abrams scales exactly to fit 1/2" CPVC pipe, which will make the modelling much easier.
Design decisions made, now I have to just get started and build the thing!