I run Vittoria Randonneur 700x35s as my standard commuter tyre and there is about a centimetre of chainstay clearance each side. I have an '05 Jake.

I have tried Michelin Transworld City tyres in 700x47!!! They were a very tight fit with less than 3 milimetres beneath the fork steerer and a couple of mm chainstay clearance so would rub on the stays when out of the saddle.

So you will be OK running 700x40 or 42. Transworld Sprint semi slicks come in that size and are inexpensive so are a good chunky tread tyre to experiment with. I run the 700x35 version on my weekend wheels and they have better clearance than the vittoria 'slicks'. I intend to order the 700x40c size when they are done with.

In dry conditions or on the road I think that you may be able to run up to 700x45. Tyre sizing is an area of hyperbole and outright lies. Most manufacturers tend to exaggerate the size.

I would really like to know how WTB Mutano Raptor comps in 700x44 fit.