yeah..I agree don't sell too early...if you must take some profit your example of 1/3 makes sense..even a tight rising stop loss on a 1/3 may get you a bit more money and limit the downside...
I bought 20,000 KCN years ago at $2.20 and sold at $3.00 whilst it was on it's way to $6.00+ after letting my wife get in my ear, if only I had put in a rising stop loss.....you don't want to take the profits too early..but I am sure you know this...