That's interesting to know.

Arberry's translation - and I read Ib Warraq's Why I am Not a Muslim, in which he dissects the Koran. He may not have a doctorate but Warraq is a scholarly author and he doubts Muhammad's existence and references many other scholars who doubt it as well. The general consensus from scholars Warraq references seems to be that of all the major religious doctrines the koran is the most incoherent and fractured, containing the entire Torah yet out of order, a swathe of christian mythology and a whole bunch of strange arabic mythologies and fables incorporating rock and star worship. Allah for instance, is initially the leading god of the pantheon of Medina, not the equivalent of El, the one Canaanite god. Oddly, Jesus is mentioned more times in the Koran than Muhammad. There are dozens of versions of the Koran though only 3 are formally recognised. 

Seems like the Acharya S of Islam.

You may want to check the relevant claims before accepting them as fact. According to Ibn Warraq's Wikipedia page, one reputable historian has claimed that "This modern son of a bookseller imprints a polemical farce not worth the 500-plus pages of paper it wastes." Not that he has the final say, but just be skeptical.

Great. My allusion to Acharya S was not without reason. I am crawling through Acharya S's book Christ Conspiracy, cataloging and investigating the questionable claims. It is a very slow slog, because there seems to be terribly bad reasoning mixed in with the good on every page. Like Ibn Warraq, Acharya S is an outsider with scant academic credentials, has remained anonymous and used a pen name for most of her writing career, publishes books of history that double as polemics against an established religion, and treats the conservative religious position as the primary opposition. Her book is also thoroughly referenced, but the key references go to outdated and fringe modern sources instead of the ancient relevant evidence.

If I were you, I would investigate the positions taken among reputable secular historians of Islam who have academic credentials, find out the arguments that they accept for the historicity of Muhammad, and see how the arguments compare. Chances are, of course, they would take the historicity of Muhammad to be an obvious and assumed fact, but some arguments are relevant ancient evidence would be discussed on the web (i.e. Wikipedia's Historicity of Muhammad). Examine the explanation for the same evidence in Ibn Warraq's book. Also, see if you can find a critical review of the book from the secular camp, though that may be difficult. There may be good arguments that come from Muslim apologists about Ibn Warraq's historical claims, though of course the anti-Islamic polemics would be a huge distraction for them.

I imagine that, in a few thousand years, after the historical evidence has been largely destroyed and Mormonism becomes the established Christian sect that dominates the world, there will be a few authors who assert or doubt that Joseph Smith ever existed, using the same arguments--the historical silences, the similarities to other mythologies and mythical figures, the historical improbabilities of the mythical character of Joseph Smith, the deceit that was central to founding the LDS church, and so on. Not that Joseph Smith is analogous to Muhammad in every respect, but I think it is a reason, again, to be skeptical. There are authors who take advantage of wishful thinking of every audience perspective, not just the religious perspective, but also the anti-religious perspective.