3 That sacked Rome too dearly did assay,
That > [Their valour] sacked > (Pa. ppl. adj.) assay > put to the proof; hence: learn, experience
4 The recompense of their perjured oath,
recompense > reward, requital of > [for] oath > [peace treaty: see HRB 3.9]
5 And ransacked Greece well tried, when they were wroth;
ransacked > (Pa. ppl. adj., as "sacked" in line 3) tried > tested (as "assay" in line 3)
6 Besides subjected France and Germany, 7 Which yet their praises speak, all be they loath,
yet > still, even now all be they > [although they are]
8 And inly tremble at the memory
inly > inwardly