Flat tappet to solid roller...

I use the Crane coated steel gears with Herbert billet cams, no problems here.
Maybe by now you might, but you probably won't hear a cam company other than Crane recommending the coated steel gear, liability issues. You can have a solid roller ground for you with a profile that checks the valve at or around the .550 , for the reasons you stated and in doing so you'll lengthen the life of the lifter because the profile for the stated rpm range will be less aggressive yet more than a fast rate solid. I do this a lot with small blocks with factory casting heads.