They aren't just 40% lighter than your DR650, they make about the same or maybe more rear wheel horsepower.
But they are race bikes. So it ain't all puppies and rainbows. Well, actually it is on the trail. But as a dual sport they vibrate worse and suck more fuel than your DR650. Plus highway riding is....ummm.....less than ideal. But they are a riot on low speed asphalt.
About carrying the oil, most of the smaller bottles you buy are marked in ounces. So unless you are finicky about exact mixtures just buy a small bottle or two to carry (in a ziplock bag) with your tools and know how many ounces per gallon to use. Where you put those tools and oil is a whole 'nother question. There just isn't much to these things for carrying enduro bags and such.
I already lost one fender pack off the back. But that was a good solution. They need so few tools that I may try another one of those but more securely mounted. All I carry is the stock slightly augmented tool roll, a front tube, tire iron, CO2 and a few ounces of oil. All of that fit in a front fender pack before it went AWOL. A backpack is probably the best idea. I just hate wearing them.