> What are the features of the 1.6 booter over the 1.4 (i.e. why bother
> upgrading?)

Once installed (and working) there's no urgent reason at all to upgrade.

The main feature beyond 1.4 is the unification of sun4/sun4c/sun4m
boot code (i.e. one binary does it all).

BTW. There should not have been versions beyond 1.5 at this point since
 there haven't been any functional changes since that version, but that
 bump (to 1.6) has fallen through the cracks.  (but maybe last week's
 bugfix warrants a bump anyway).

-pk