The study investigates the rhythmic organization of speech in two discourse types—reading and spontaneous speech—among native English speakers from Australia and New Zealand, represented by 38 speakers (19 from each country). The audio recordings, totalling 02 h 46 m 01 s, are taken from the IDEA corpus [11], balanced for gender, age, and dialect of English. Applying the set of eleven metrics collected in the Correlatore software [12], we discovered a statistically validated differentiation in rhythmic patterns primarily between discourse types rather than the dialect, which confirmed the existence of ‘rhythmic diglossia’. Thus, the rhythm class division of languages into syllable-timed and stress-timed categories, associating English with the stress-timed type, becomes questionable due to the influence of various factors, including dialect and discourse type.