Shimano BR-R650 long reach calipers compatible with Paul Components Canti Levers?
Super SLR mismatches in this direction result in mushy feel and needing to get the gap between the pads and rim smaller than normal to avoid bottoming out the lever. You'll get brake rub from wheel flex and out of trueness that would otherwise be negligible. It's a lesser version of the problems you'd have putting a v-brake on a short pull lever. It's enough to notice but not so bad it doesn't work. You'll have to live with having taken two nice components and made a mediocre system out of them. It will feel and perform way better if you just get a Tektro brake of the same reach and call it a day.