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This has been a dilemma for me as well. I have been experimenting on the cable with a demo FX account. If you are using any trend following system that uses moving averages, then the longer your time-frame is, the more accuracy you will have. I am currently manually back-testing some M/A based systems on Meta-trader, and I've found that the 5 minute chart filters out many bad trades that you'll get on the 3 minute chart. At the same time, you won't get the lag that you get on a 10 minute chart. As far as stop losses are concerned, look up Linda Raschke's video titled "How to Use Stops, Why Trade with Stops, How to Determine Stops". She says that the wider your stop, the better your accuracy. She recommends an initial stop of 3 ATR. She also tested time-based stops on the daily chart, and she found that you should exit a trade if it doesn't work out within 7 bars. I reckon that would work well on a lower time-frame as well.