Runnable range is based on Squires' book.
Squires lists Upper Jamestown as a IV+/5.0, and Lower Jamestown as bigger and badder--likely a portage. At 1700 cfs, I found that I wanted to walk Upper J, but I found a far-right sneak at Lower J.
If you don't want to paddle to the Parmenter Site, you can take out 250 yards below, at a hard-to-find (from the road) dirt road.