Are you entirely sure about that? Do you mean percentage by volume or percentage by weight? Does OS mean by volume or weight? And are you sure about the percentage that your manuals state?

For the 46AX, Hobbico says 16%. For others, they list up to 20%.

Omega will work fine. I've used it for years, along with Morgan's Cool Power. I've also used Sig Champion and Wildcat, and probably a few other brands, too. The common blends from the large manufacturers will all be just fine. What you have to watch out for are the blends from the fellow who buys ingredients in bulk and blends his own.