I grew up near Rutland and today was a uniquely beautiful day. I ran the reservoir (including the Hambleton peninsula) supported by my Dad and son on their bikes. (which is mostly why I put Supported option - although I carried my nutrition and any can do this unsupported. There are a couple of great cafes around the reservoir if you need them)
We are in the middle of a heat wave at the moment and the plan was to start early (after a drive up from London) but by 8.30 it was already in the 20s and rapidly climbing to an eventual (too hot) 33+ degrees. The route mostly follows a clearly waymarked route around the reservoir. Some of its on gravel tracks, some paved and some through wooded forest. Much of it is exposed - which does mean that you get an almost unspoilt view of the water for the entire run.
Route with peninsula is 22 miles (35 km) and one loop of the reservoir. No real advantage to do it clockwise or anti
If you have never been to this stunning part of the UK I thoroughly recommend that you make the trip. This trail is fast and free flowing. Thanks Dad. Good luck