I can't help with brass to OEM or brass to carbon fiber, but I go from OEM to carbon fiber.
(I have about 500 miles on the rebuild if this matters on my opinion)
My 5-speed had OEM blockers in 1-5 and brass in reverse and I don't know what it had for fluid. It now has carbon fiber 1-4 and brass 5th and Reverse and GM syncromesh with friction modifier in it.
Besides the 2-3 shift, I don't think I can tell the difference. When I shift from 2-3 about 1 in 20 times it will grind. 1st and 2nd still need extra muscle to get into them before and after the rebuild.
I did speed shift it once racing on Sunday and 1-2 had just a little grind and 2-3 had some grind. I'm hoping the blockers are still breaking in and this will get better.