Steve, you don't need carbide! ZA12 machines beautifully with high-speed steel, the sensation I have is sort of half way between mild steel and Al, Al with the crispness of steel, when I first read about ZA12, it was described as "machining like a dream" well honed sharp tools with what would be too fragile for steel points work well. It is softer than one would think from filing it. Sharp coarse files work better than fine ones, the coarse ones can get into the surface whereas the fine ones load up and skate. For machining, the same is true, you need them sharp and coarse, points that can get into the metal!
I think your going to enjoy the next phase, I'm looking forward to hearing about it!
Regards, Matthew