frequency response in entirely driver and enclosure dependent. If you check the website for the specific speakers you're talking about, most reputable companies will let you see the charts for their speakers.
That looks pretty good but there's no single forumla that will work for every system. Thats a good guide though. Personally, I like to cross tweeters over no lower than 3K Hz to get them out of the vocal region if possible. This is a resource I used when designing a pair of bookshelf speakers with a peerless midbass driver and morel tweeter: