On a Trek DS, I've got the following:

Velocity Dyad 700c rims
Shimano Deore XT 36H hubs (135mm rear hub spacing, 100mm front hub spacing)
DT Swiss 2mm straight-gauge spokes
Continental Tour Ride tires, in 47-622 (28x1.75)

Very highly recommended. Stout and great ride quality. Noise-free, despite a commute that's got numerous potholes and with several minor to moderate strikes already. The 47-622 sizing of the tire makes it difficult to fit full-length fenders, so 40mm sizing would be smarter. Am north of 200# myself, and it works great. But I should think it would handle a 300# rider without any problems, unless you're tearing it up on rougher terrain more suited to a proper MTB.

EDIT -- BTW, this wheelset was found, brand new, from a brick-and-mortar shop that sells some of its overstock and custom-but-not-sold items on eBay. Price was sub-$200, for the wheelset, plus $25 for shipping. A pretty good deal, all things considered. Having this done up, new, at a local shop would have been significantly pricier, for the same setup (based on their quote). Deals are out there, if you know what you'd prefer and hunt around a bit.