I have ran both in my avatar truck, both ran nearly identical motor times, the 377 was a tad faster on the bottle. I prefered the 377 simply because I like to twist mine, and the 406 ran out of breath about the time the 377 was just starting to sing. If my 377 stuff was good, and I had another block, I would go back with it, if I had to buy the stuff anyways, I probably would still do the 377, but if you prefer the 406, then it would be the time to do that. All boils down to what you want, and if I was unhappy with the sellers response, I might send them one more message that I was going to throw them under the bus...