Goat Fell sounds great in theory but I wouldn’t recommend it. Unrelenting climb up the first third followed by and unrelenting push / carry / drag to the top. You would need to be at the top of your game to ride back down it, and its not my idea of fun!
You can follow the tourist route up to where the treeline ends and then pick your way back down through the various bits of single track either side of the main trail but there is better riding elsewhere on the island.
There is some really great bit of riding on the arranbike link above. Second the Clauchland hills its a great bit of trail.