You can NEVER forget this performance.
They were, if not my first then one of them, JPOP groups that started me. I'm only 16, so I must have been listening since first grade or kindergarten... (suprisingly, I'm not fluent! Ahaha)
But yeah. I even remember lip-synching songs when I wanted to in like, second grade. Ahahaha. They were one of those groups where if you haven't heard of them, then you were like, a dork. Ahaha. I would have to say besides ZONE and Morning Musume, this was the one true group where EVERYONE knew. No matter what, whenever you turn on a Japanese Music show, there was some reference to them.
One tidbit: None of the singles they released (while they were intact, not reunioned) sold less than 500,000 (and I believe that was their first single that set the hurdle). Many credit that to Eriko and Hiroko, the two front members (especially Hiroko, who was 13 I believe at the time of their debut). Imagine voices as strong as a studio version (if not stronger) LIVE WITH DANCING. That gave them a LOT of credit.
But yeah. They were THE group. I would say that they ARE the most successful girl group in the history of Japan given their lifespan. Although Morning Musume is still going strong, and even though I fully support them, I think that even they can't compare to SPEED. Not even ZONE or Pink Lady.