Actually, I have no idea. I know 7005 tubing doesn't need heat treating but can benefit from artificial aging. Usually, 6061 needs both solution heat treating as well as artificial aging, but I don't know about this 6066 stuff. I'll take a wild guess and say that maybe the tubing is already at T6, then welded, then artificially aged - avoiding having to solution heat treat the entire bike? I dunno. I've been ignoring Aluminium for a few years (can you tell? ) I'm not really the guy to ask about off-the-shelf bikes....I pretty much hate them all

Just do like everyone else and buy whatever is cheapest