I presume that we are talking about magnetically soft alloys.
This somewhat depends on the field strength and temperature. At very high field strengths the highest saturation is at lower Co contents, say about 35% (Fe2Co), this is also true as you go to temperatures lower than room temp.
If you cut or machine a part it will need a good anneal to recover maximum saturation.
Additions of V or Cr help to lower the initial permeability, but lower the saturation.
I believe the highest saturation induction levels at room temp in commercially available material is about 50% iron cobalt. These can get to over 2.4T, pure iron not quite 2 T. Go to Cartech's site, they make a wide variety of magnetic alloys. There is a ton of literature on the subject.
No, at high field the highest saturation is Fe2Co, 34.6 wt% Co. I have no idea if this material is commercially produced. I made some years ago (vacuum melted from high purity metals) and alas I don't have any.
Even high purity Fe has a tough time topping 2T. In high purity form this alloy has been reported at 2.6T.
I've never seen anything commercially available in the 35% Cobalt range. 48-50% is common, then I've seen 27% & 17-18% but these have only about 2.2T saturation.
If 35% cobalt is so good why doesn't anybody make it? 2.6T would be worth a fortune.
Hiperco 50 (from carpenter) is the highest saturation alloy I know of. This is a 48Fe Cobalt alloy - in essence it is the cobalt crystal doped with the most iron it can possibly hold with some stabilizing elements. HOWEVER:
1. Can be hard to get in useful forms. Scientific Alloys is the only distributor I've found that sells it in small volumes in something substantial.
2. It requires a very specific anneal prior to use, and after all machining. Without it, the saturation induction is a fraction of its theoretical.
I just got off the phone with someone from Scientific Alloys in Rhode Island.
He really took the time to understand what I wanted to make and gave me tips on how to manufacture that. In the end he recommended pure iron versus hiperco for its ease of machining.