Houston...we have a problem.

OK, after a little modification I've measured the Berlin branch at a 3.9ish % grade, and the part that ties into the helix will be about a 3.5ish % grade. With the curves it's enough to make it difficult for the locomotives to get a train up the grades.

I tested the Athearn RS-3s. First of all, I didn't particularly like the sound of the motor. I tried two of them and they sound the same. So I'll have to see if one of my modeling buddies can help with optimizing and maintaining them. They had trouble with 5 cars.
An Atlas RS-1 could pull 9 cars, but struggled up a portion of it (obviously the grade isn't even, so I've got to work on that as well. That might help). The Holyoke freights will come up through this section of the layout, so the RS-3 will need to be able to get up that portion.

But the biggest problem is that the most frequent locomotive to use this trackage will be the 44-tonner. And the best it could manage was 2 cars. In fact, when I had 5 cars on it and helped it get partially up, the weight of the cars was enough that they pulled it back down the hill.

So, what are my options? I could forego bringing the Holyoke freights up through this track. Operationally it wouldn't really matter if they came 'from Hartford.' If I did that, I could raise the Berlin branch and and simply take that off the back of the Hartford branch. Again, it wouldn't really impact operation much. Then the Berlin branch would simply be a track that runs off the edge of the layout. Overall it would be workable, although not really what I'd like to do.

The Holyoke freights would be OK double-headed. And that's prototypical, at least some of the time. The Berlin branch is actually a 2% grade on the prototype, and they even double-headed steam because of that. I don't have enough RS-3s right now to double-head all of the Holyoke freights, but it's doable and my preferred option for that.

Running two cars at a time up the Berlin branch with a 44-tonner may not be too far fetched either. In the Alco operator's manual for S-1/2, RS-1s for a 660 hp locomotive on a 2% grade can haul approx 326 tons at 10 mph and 667 tons at 5 mph for a 99-ton locomotive. The 44-tonner is an 89-ton locomotive with 380 hp.
Math was never my strong suit, but 326 tons divided by 40 ton cars yields 8 cars. Although I'm sure that it's not a linear equation, I'm coming up with a little less than 5 cars for the 44-tonner. Since everything is selectively compressed (including train lengths), 2-3 cars isn't horrendous. But I'd prefer 4-5.

Another possibility would be traction tires, at least on the 44-tonners. I've never used them, and I dont know if I can put them on only one side. If so I could use one tire on the side of the locomotive that's always facing away from the viewer.
Another issue with all of this is that there is a similar track on the other side of the layout. But that's the mainline entering the helix which could be a much bigger problem. It's a longer track, so I'm hoping to avoid these issues over there.

So it's time for a bit more experimentation...