This is interesting...I've always tried to keep hole locations in areas that are 2.5% slope or less. According to this graph I found on Twitter, green speeds in the 11ft range can accept hole locations in the 3.5% slope range. That seems a little steep to me and most golfers couldn't stop a golf ball at that speed on 3.5-4% slope. Slope is determined by rise/run. 4% slope would be a 4' drop in 100 linear feet. In 10 feet, it's approximately 5" of fall.