I know that John - usually - does no beta versions.
BUT this one may be worth an exception since
a) 7-Zip v.4.42 is quite old meanwhile and
b) the actual 4.51 beta is not a "real" beta but an advanced version close to final (it runs veeery stable like all its predecessors and does - besides some new functions - contain lots of bugfixes over v.4.42)
Maybe worth the hassle of some pre-release Beta testing since it should be easy to update...