Bottom Line Up Front (BLUF): Suno V5.5 is the previous flagship of the Suno line. It delivers an even, predictable result and holds the genre well, so it suits you if you already know the sound you want and prefer stable quality without surprises.
V5.5 balances expressiveness and care: the vocals are clean, the arrangement does not fall apart on long tracks, and the style you describe is followed precisely. Many tracks generated earlier were made on this very version.
Like V6, it offers a custom mode: your own lyrics, negative tags, an instrumental-only take, voice choice and a duration of up to six minutes. That is handy for songs with your own structure and unusual length.
V6 is newer and usually more expressive; V5.5 remains a reliable pick for a familiar, even result.
Yes, in custom mode the duration can be set up to 360 seconds.