The remarks from ZMC888 are spot on.
With newer, EFI equipped bikes, it is a mission impossible to get better curves without running it on the dyno for several sessions.
And even then, only a slip-on will hardly do anything for increasing power.

Basically, the additional power from changing to a more open pipe is only in your mind.
The louder or deeper sound seems to make it faster, but actually it is not, just a little mind game.
We picked up a Ducati last weekend, still fitted with an original (quiet) factory exhaust.
It's output is identical to mine, but I guarantee you that riding it is not half the excitement of an open system, and hence it feels very very slow.....

That Benelli certainly deserves a more open system, but don't expect it to become stronger.
On a sidenote, adding just open pipes will not do much harm at the bike, other then that if will backfire a bit more on deceleration.
Nothing to worry about.