"My weight is around 70 kg. I mainly use my 4.2 and 4.7 sails between 20 knots to 34 knots. Could you tell me if the Pocket Wave 62 L from 2008 is enought for me, or is it too small? I don't know, what is the best choice for me?"

I would suggest the bigger board- but I like bigger boards. I think you are right on the edge of either board- what board are you using right now? The new Pocket’s are really nice- I would get the new 69 if I were you..... A lot of the small guys on Maui are using them and loving the way they are working