Facemil vs flycut for engine heads where facemill wont cover head in 1 pass.

Sorry to open an old wound.
I did scour the forum for the last 2 hrs. (Honest)
AND I just found a product to suit my machine.

Figured I'd ask the same question in a more reasonable way then i did last time. (Sorry mod)
I have a way now to fit up to a 3 inch face mill on my my CNC and remove an insert or two if necissary.
I want to skim race bike heads. They are 160mm wide.

I can use a big 200mm home made fly cutter someone who is good at making them will make it for me should I ask. (I can run my spindle OK at 1500 rpm which appears to be ok.)
Or I can do 3 or so passes with a good quality 2.5 or 3 inch face mill.

I understand you may see the crossover line on the face mill, but you shouldn't feel it, and the tolerance to it should be almost negligible right?
If it will be fine I'll buy a face mill. If not, i'll try a fly cutter but i bet it's going to chatter with that 1/2 inch shank. I just don't see that anyone has done it with a face mill anywhere i have checked and checked. They have ALL been over the size of the head.
Either way I"m spending money. Any advise appreciated.