Thanks a lot to all for the infos: I can now make an educated purchase choice in a few days with all criteria clarified.

Thanks for telling me about the possibility of changing yourself your account name, I didn't know that.

About FNAC: yes it does exist in major cities but I dislike it (basically they sell not so good expensive computers to urban busy ignorant people who don't care about budget nor specifics, and salespeople are simply ignorant about what makes a good PC and pretty arrogant sometimes because, selling books and concert tickets, they think they are part of a "cultural institution".

Anyway, I have a personal horror story about FNAC: when I was a student (id est young and very casually dressed), I asked a salesman to give me more details about THE ultimate enormous and horribly expensive short wave radio receiver (price was around 5 months of a standard salary then), the salesman looked at me literally from toes to head and replied: "Why are you even asking, you can't afford it!" and just left...