Well, just adding Sterling upfront front made significant improvement as it gave us pace up front and runners behind the opposing back 4. Its not Sterling's natural position and he has not exactly been prolific or cutting edge, but it has allowed our football to flow much better and we are starting to look ourselves again.
Berahino is a player who has that pace, runs in behind and is natural in that position. Berahino would be more prolific and instinctive in that role and would chip in more goals.
I think we have learnt this season that style is very important for us when signing players. An above average player who fits our style is better for us than a better player who doesnt fit. Out of the other strikers available, including more experienced ones, many dont quite fit stylisticly like Berahino does. Lavezzi maybe, but not as a lone striker IMO, which I think we must consider looking at Sturridges fitness and the increase in clean sheets with this current formation.