I would, with great pain, say that the sentence is written correctly from a prescriptivist standpoint. But, I would immediately point out that it is not what many native speakers would say, and I believe there is some shift in the use of are (instead of is), in a sentence like this. I have heard many native speakers say 'Speed and control are what are important in email relationships.'
I like Delphi's solution better, but even then, I've heard many native speakers say things like 'What are important... are speed and control.' I have some friends who argue that what represents plural concepts, and that's why people are treating it as a plural pronoun. I have other friends who are apoplectic about this, when it's discussed, but even they agree that more and more people are using this plural construction in normal speech.
Where does that leave us? Arguing over subject verb agreement.
Jin, you are welcome. Cypherpunk and Delphi have both given you good answers. In thinking about Cypher's observations, I too have noticed that many people do say things such as "What are important are speed and control." I think that speakers who use this construction use "what" to signify "those things". Thus:Owlman5, thank you. You and all others above have provided much food for thought. I will pass on your ideas to my co-workers.