In reply to PaulTclimbing:
(Caveat: Am not a fell runner!)
Would think it depends on the weather. There's a lovely spur which gets you from the top of Commedagh to a long way down the Glen river valley. Go across and join the track by the river. It's a great walk. However I've only ever walked it and don't know what it would be like to run (i.e. how uneven it would be). Would not advise this at all in poor visibility - there's a corrie on each side! (Though there may be a track now? It's decades since I've been.)
The default option is definitely to run down to the Donard/Commedagh col and down by the track, i.e. Glen river valley. In poor visibility, this would be your safe bet.
I used to climb with a guy called Denis Rankin, who sadly died running in the Mournes (his heart gave out). I think there's a memorial run to him now. He was in a local fell-running club who were very keen. If you had a google around, you'd probably find them and they'd give you expert knowledge.
Always loved Commedagh ('mountain of the watching'). Enjoy your run.
Mick