Time has already told, I think. It´s an interesting way to complicate the game but objectively White is slightly better.

No, the Gallagher is this sort of thing:  6...Nbd7 7. Nc3 e5 8. e4 ed 9. Nxd4 Re8 10. h3 a6. 

Incidentally I recently noticed Sam Shankland giving 10...a6 a "?!", and saying that he thinks the old way of playing (with moves like ...Nc5, ...a5 and ...c6) is better.  I would think that both are generally regarded as "+/=" with best play, and so it should be difficult to make such a distinction.

Maybe transpose to a Grunfeld? It is what a lot of kidders do anyway.

When aggressive means creating attacking chances against the white King then it's probably 1.d4 Nf6 2.c4 g6 3.g3 Bg7 4.Bg2 0-0 5.Nf3 d6 6.0-0 Nc6 7.Nc3 e5 8.d5 Ne7. This variation doesn't have a particularly good reputation, doesn't score very well plus White can avoid it with 7.d5.

So perhaps the best candidate for aggression is a transposition to some Benoni. 1.d4 Nf6 2.c4 g6 3.g3 c5 but White does not have to play 4.d5, as 4.Nf3 is good enough. The same is true if Black plays ...c5 later.

If Black is willing to play the Pirc/Modern another option is to postpone ...Nf6. 1.d4 g6 2.c4 Bg7 3.g3 (3.Nc3 d6 4.Nf3 Nc6) d6 4.Nc3/4.Nf3/4.Bg2 Nbd7 and 5...e5 heading for an early ...f5.

May be You know that I'm only a club player and I'm lurking in this site for many of you are really much better player than me.

I need a suggestion: according to your experience what is the most aggressive variation for Black against the Fianchetto Variation?

Thanks in advance.