Marathon Supreme are quite light, even in the fat 50 x 559 size. I have these on my two Raven Tour bikes. In my experience they cope OK with moderate off-road use on paths and tracks, and are very good on tarmac roads.
Marathon Supreme also last a reasonably long time, not yet worn out any, and still plenty of tread on the longest-serving pair with more than 9,000 kms on the front and 5,200 kms on the rear.
Downsides are the high price, and I reckon the light sidewalls will be more likely to suffer damage if you hit broken glass or sharp rocks.
Duremes (which I also have, now on a visitor bike) are slightly heavier, slightly slower, and seem sturdier, so maybe a better choice for expedition touring.
I recently changed the tyres on my old 650B utility bike, so have been able to do a direct comparison. I had been using 44 x 584 Marathon Standard for several years, these are a good sturdy tire but a bit on the heavy side. First of all I used 42 x 584 Marathon Supremes, these were significantly quicker, then I fitted 50 x 584 Marathon Supremes, not quite as quick as the 42 x 584 bit still quicker than the 44 x 584 Marathon Standard. When riding off-road, the 50 x 584 Marathon Supremes are much better than either 42 x 584 Marathon Supremes or 44 x 584 Marathon Standard, and are also more comfortable.
The 42 x 584 Marathon Supremes went to my wife's bike, where she found them a significant improvement over the 44 x 584 Marathon Standard she had before. Clearances on her bike are insufficient for the 50 x 584 tyres.
