What Java versions are required for which versions of Pentaho?

I am looking to make an upgrade from PDI 4.2 to 6.0 (or some other newer version, should 6.0 have problems). If I upgrade the current JRE from 6 to 7, will the Pentaho 4.2 still work? (More specifically, do both 4.2 and 6.0 work with JRE7?)

I am assuming that installing JRE 8 will break the use of PDI 4.2, so I am wondering if installing JRE7 can allow some concurrent-running.

Thanks all.