Well, not the Windcheetah - it has too many wheels. The best use of a third wheel is to stop a fully enclosed machine from falling over when it stops!
HPV racing does not conform to a systematic set of rules such as that imposed by the UCI on upright racing. Each country has its own system of machine categories, and its own specialities. For example, streamlined road racing
bicycles like
this have been done better in Britain than anywhere else; the Dutch like
velomobiles; German-speakers like
massive tail fairings (but still class their machines as "unfaired"), and
Americans have a class for "faired, but you may not move any body panels to get in" which they call Super Street.
If you agree that "unfaired" can include a fairing
behind the rider, I reckon that bikes with a big, close-fitting tail fairing like the Birk, Razz Fazz or
Mike Burrow's one-off Ratracer Special are currently the fastest road racing bikes; if not, I concur with McD that very low "splitter" bikes like the
Nocom and
Cobra are the state of the art among machines that do corners. And you can buy one; whether you would want to ride them on public roads is another matter.
However... splitter frames could be construed as fairings - you see how difficult it is to impose catogories on a sport in which innovation is so important? If you insist on absolute unfaired purity, Sean Costin's (extremely low) Monkey Hand is very quick over 200 metres (it's shown 3/4 of the way down
this page); and
Rob English's Hachi is light, aero and allows a riding position which is possibly better for generating power than that of the very low bikes.