Everybody's position in the weight vs. robustness spectrum will, I'm sure, be different; but for Audax, I would suggest:
32 hole Sun Ringle UFO 559 rim, Ultegra hub, laced 3X drive side with plain guage spokes, radial non-drive side with butted spokes (which helps to equalise spoke tension between dished and non-dished sides). And a Stelvio.
The rim is light, which means that peripheral revolving weight is minimised. The "extra" four spokes are well worth their weight for reliability. If you want anything significantly faster but still "bombproof", you'd need tubs, I reckon; I don't really see Audax and tubs going together. And I don't know of any robust 650C tubs, anyway.