I did the Sugar River in Newport, NH last Sunday with the OC1 group at the NHAMC Whitewater School. We paddled the section from Corbin Road to Route 103 in Newport. The river was at a nice level – 3.3 ft, 1200 cfs – hit it just right. I'm told that it needs to be above 3 ft for a fluid run. Nothing tough about this river – easy class II with one class III drop – Sweet Tooth. Few pictures here: http://www.flickr.com/photos/eckilson/sets/72157633300195428/
3' is as easy as the Sugar gets. The whitewater kids run it down to 2.5 but it gets pretty technical/boney. 4' is a little sweeter for surfing. 2' is a perfect poling level.