Every time there is a beta, there is the possibility that it will be the release if there are very few bugs reported. I believe that 5.1.7 will be the official release of the v5.
I think the plan it (emphasis on "think") is for 6.0 to be ready or nearly ready by ACUC, which would be June. Given that many will want others to take the leap first, it may be a good idea to go with 5.1.7.
