The 275/70/18 (33" x 10.8") might fit okay. They'd rub if you went offroad and flexed the suspension (need a lift) and they might rub on full lock turns (need wheel spacers or new wheels). The 285/65/18 (32.5" x 11.2") would be less likely to rub offroad when flexing, but more likely to rub on turns.
Frankly, unless you really love the Sahara wheels, the standard advice on this forum is to just get new wheels and tires. Tires for 18" wheels are very expensive. Tires for 15" wheels are much cheaper. If you go with a 15" wheel (that fits . . . not all do) you'll likely be able to get both new tires and wheels for about what you'd spend on new tires for your current wheels plus spacers. In fact, if you then sold your Sahara wheels/tires on Craigslist, your out-of-pocket cost would probably be a lot less than just new tires/spacers for your Sahara wheels.
Alternatively, scan Craigslist for a set of Rubicon wheels/tires. They have a more aggressive tread and will be a perfect fit.