Hi NachoOne Welcome to FAOL. I agree with the five weight recommendation but I want to address what you said about arm fatigue. Unless you have some physical problem with your arm it should not happen that quickly. Try to get a good caster to watch what you are doing. If that isn't possible try watching the Mel Kreiger videos linked in this thread:

http://www.flyanglersonline.com/bb/s...-wrong-casting