I have a Life Like SW1200 that has been working the layout all by itself for years. It wasn't until I bought a Micro Trains SW1500, that I realized what a masterpiece that SW1200 really was. They both use virtually the same mechanism, but with some added weight on the SW1200, it could pull like crazy as compared to its sibling SW1500.
Ray Eiser installed a decoder and added some Tungsten putty to the SW1200 (including front and rear headlights, and hardwired pick-up), before it ever went into service on the layout, so I never thought much about its pulling power. Once my new SW1500 arrived, I was really amazed at what a difference there was between the two. It has been on the to-do list to have a tug-o-war between the two and see just how much difference there was between them. I finally slapped together a couple vids and posted them on You Tube.
Check out the video links to see just what a little bit of extra weight can really do for your locomotive fleet!
You Tube- SW1500 vs SW1200 Tug-O-War
You Tube- SW1200 vs SD9 Tug-O-War