Welbeck's footballing ability is his main strength, I doubt he'll ever be a killer infront of goal. His passing and link-up play are easily as good as Giroud's IMO. And he'll add much more pace and dynamism to our front-line. A forward like him is far better for a playmaker like Ozil too.
I'd personally sell Giroud, bring in Welbeck as a back up striker if he's available and a top striker like Costa or Cavani.