There are several ways you can represent "fast" in a logo. One way is to "italicize" the logo (text and/or graphics) which conveys movement. The more you angle the content, the more speed is implied. However, too much angling could distort your work.
Adding lines behind the movement might help. See GiantCowFilms example for this.
You might also consider only angling part of the logo, especially if it naturally fits that part of the logo. Italicizing words like "express" or "fast," if part of the company name would imply speed.
Another approach might be to add a slogan or other text that can imply (or outright state) that the company is fast.
Finally, you can find a symbol that gives the impression of the company being fast. Jets are a great approach but often do not fit the company's business. Think of other ways you could show "fast," even if they are not entirely realistic.
Attribution: The hand extending from the computer monitor design was downloaded from FreeVectorArt.net. It is being used under the Creative Commons Attribution 3.0 License. It was designed by Vector Open Stock.
I hope these ideas help.