Haven't been on in in a few weeks.
There is TOO much data that if you use a Balancer, Sim-Angus or a Composite bull you DO NOT lose heterosis and the calves should be much more uniform. It has been posted on here before.
It is true that F1 crossed have more hybrid vigor and the next cross you will lose some of the hybrid vigor, but after that it should be maintained. The only thing to keep in mind is to use outcrosses and don't linebreed. When you do, some more hybrid vigor is lost.
I think that almost any breeding program comes down to management and breeding selections. I have seen some herd that use sim-anugus for several generation and have several of the cows that are producing choice carcasses. I see other herd that are not as good a quality and therefore the quality of the calves that are produced aren't as good either.
One advantage to using bulls of mixed breeds whether it is a 50/50, 60/40 or a 25/25/25/25 such as the stabilizer is that the results should be more consistent. If you take an animal that is say 50% Gelbvieh and 50% Angus and then cross with another breed, then you have a much wider swing in the genetic makeup of the animals.
If the base herd is not good quality cows, then using another breed will probably show more noticeable improvement. Again, management and breeding decisions are extremely important.