Early request to suggest keeping these versions in the repository long enough to stabilize. Security fixes for PNM in -50 caused issues breaking tests of media-gfx/gscan2pdf using xc:black an xc:white: https://github.com/ImageMagick/ImageMagick/issues/1636 I've only used and tested ImageMagick 7 but fixes were committed to ImageMagick 6 too.
Fixed by: https://gitweb.gentoo.org/repo/gentoo.git/commit/?id=057e483d6a07ee2e3f98371318d5aeef6d58102b