Sorry Tim, never fished there, I know some of the lochs a bit more to the north...
One piece of advice I can give you is to keep moving! Don't change your flies, change your the bank you're fishing them from. I make 5 casts from one spot, then move to the next when I don't catch a fish. When you do hook up, stay a bit longer for number 2 or 3, but when you only catch small fish: move on!
And take Soundmixer's advice, big flies for big fish.
Good luck,
Jeroen