To be honest, this sounds like the kind of book I'd not want, precisely because it's trying to do two very different things at once.

If a person is learning about Perl for the first time, then there's no reason to use the transition from 5 to 6 as a background. They don't know 5, and trying to teach two variations of a language at once is dubious pedagogy to be sure.

On the other hand, if someone knows Perl 5, but isn't willing to go out and learn about 6, then probably they've already made up their minds that Perl isn't for them. After all, Perl 6 isn't that big a change -- it's not like it's going to wake up one morning and realize that it's C++.

I've been using a humble 31-page booklet by John Vromans of the Squirrel Consultancy on Perl 5 for quite some time (is this the pocket reference you're talking about?). And personally I like the two extremes: a resource that's quick and to the point, and a set of resources that go deep, like the Camel and our Monastery.