Powerful enough the fight the world destroyer level characters. I don't really care how fast.
Fighting is a lot more about cleverness and ingenuity than it is about raw strength. Some beings who have very little in terms of direct power become serious threats, whereas others who are ridiculously powerful become fodder because they're trumped by a good ability that's used well. For example, one being has the ability to channel magic through a series of painted runes. But the various combinations and creative decisions led to that being one of the strongest ones.