If we get Sahin then I don't see why we can't challenge provided Giroud doesn't flop.
Even Adebayor got 30 goals for us. Even Bendtner got 15 goals in one season. Provided your not a bellend like Chamkh, I reckon our strikers will get the goals we need. And with Sahin and Carzorla pulling the strings in the middle of the field with Wenger's guidance we must be certain title challengers.