>and what about speed ?
>I made a test and seems like append was 4 to 10 times slower

If you're asking about speed then "append" also have many variations which might be the fastest and way to go. I mean, asking about speed, you sound to be doing many append/inserts in a loop.
PS: I don't know your testcode but I've seen so many ppl unnecessarily using multiple replace commands where just one would do. Gather is also another replace like command.
Cetin