I did some more helix trsting today with a “heavy” freight of 25 cars plus a caboose. The 3 units on the head end pulled the train ok, however the locomotives were much happier with a 2 unit set of helpers cut in 16 cars from the head end! Everything went smooth, and nothing ended up on the floor, which is good.
Photo shows the freight near the current “end of track” with the helper set visable in the distance
And the head end with the tail end almost directly below the power. I ran the freight backwards down the helix several times, thinking that if everything could be pushed down the hill without ending up on the floor then going up hill should be easy!