Wenger's not-so-secret £16m plan
Calum Chambers was signed by Arsene Wenger after playing every single game of his professional career for Southampton at right-back. So where does he play on his first Arsenal appearance? Centre-back of course.
The England under-19 international has got the physical capability to play the position, but it promises to be a steep learning curve for a player unfamiliar to the role.
For Southampton's youth teams he played in central midfield, so he's clearly versatile and willing to adapt to the demands required. It's just a big gamble on Wenger's part to invest £16m on a player who's never played the position he wants him to play. Not everyone can be Thierry Henry.
Chambers was rarely troubled today by a largely toothless Benfica attack, but when called upon he looked comfortable.
But what we really learned today was the fact that Wenger sees him as a centre-back rather than right-back - we actually learned nothing about whether he's good enough. That will come when the Premier League season starts.
Joel Campbell is definitely good enough
The Costa Rica forward played on both flanks today, and while not everything he attempted came off, he showed enough for Arsenal fans to feel confident he can be an effective contributor this season.
The only problem is Arsenal are extremely strong in his position, with Podolski, Oxlade-Chamberlain, Walcott, Sanchez, Ozil, Cazorla and Gnabry all vying for three attacking midfield positions.
Campbell is a different proposition to all the others though, and that is good news. Quick and strong like the Ox, but with a few more flicks and tricks, he's got the finishing ability of an out-and-out striker - as evidenced by his smartly taken first-half goal.
He ended up with just one, but laid on a few more in a perfect introduction to life at the Emirates Stadium. Wenger should resist the urge to farm him out again.
Nacho Monreal is not a centre-half
I fear for Nacho Monreal. It's just difficult to see a place for him in this squad beyond as a back-up for Kieran Gibbs - and as a 28-year-old one-time Spain international, I doubt he's too happy with that role.
Because this experiment at centre-half should not be repeated in any meaningful game. He didn't do too badly, but he did not inspire confidence either and was beaten to the ball by Bebe for Benfica's only goal. Yes, that Bebe.
Shaky on the ball, and out of position on occasion, it's too much to expect him to contribute in a position he's never played before. Which means, should Thomas Vermaelen leave, Arsenal need to sign a replacement if they don't want to put too much pressure on Chambers.
Yaya Sanogo is so confusing
Yaya Sanogo was, largely, not very good last season. But he's young, he'll be 22 in January, and he scored four here. Yes, FOUR. Three were tap-ins, one was very well taken. But which Sanogo will Arsenal get next season?
The gangling Frenchman whose first touch rarely led to a second, or the goal machine in action against these Portuguese opponents? The weight of evidence suggests the former, but this was real progress in the right direction.
He looked rough around the edges last season, a physically gifted athlete but not a footballer. If there's one manager capable of smoothing out the kinks and fashioning a centre-forward out of these raw materials, it's Arsene Wenger.
Yes, it is just a preseason friendly so we must exercise caution - I'd still be worried if I was an Arsenal fan and Wenger was relying on Sanogo in the event of a long-term injury to Giroud. Because let's not get carried away, three of the goals were from a combined nine yards.
Actually, let's get carried away - Yaya Sanogo just scored FOUR!
Hector Bellerin is the future
So if Calum Chambers has been earmarked as the centre-half of the future, who's the back-up for Mathieu Debuchy?
Well it could be Hector Bellerin. The Spaniard enjoyed an electric opening 15 minutes against Benfica, terrorising Eliseu, who was replaced shortly after by Benito. He was complaining about a groin problem but it could easily have been twisted blood.
Bellerin was up against a tricky customer himself in Ola John, but marshaled him well. Still just 19, the former-Barcelona starlet also set up Campbell for his first goal. More than anything else, he showed going forward he's a real talent. Definitely one to watch.