This article is part of Football FanCast's In Numbers series, which takes a statistical look at performances, season-long form and reported transfer targets...

They were centre-back partners in Chelsea's shock 2012 Champions League win over Bayern Munich.

Once again, they lined up together in the Blues' FA Cup final defeat to Arsenal in 2017.

They were also teammates as the Londoners secured the Premier League title that same year.

Now, however, David Luiz and Gary Cahill are playing for different London clubs in Arsenal and Crystal Palace respectively, and find themselves the topic of a particular debate sparked by the BBC's Garth Crooks.

Crooks wrote in his Team of the Week segment:

"It is coming to something when Crystal Palace fans start 'insisting' who I should put in my team of the week. Just what it has got to do with them I don't know.

"However, I did find myself bowing to the wishes of one of their followers who was mightily impressed with Gary Cahill's performance against West Ham.

"He also went on to tell me that he couldn't understand why Chelsea had let him go when they obviously need his experience in view of who they are currently playing at the back.

"He then went on to say, "how could Arsenal pay Chelsea £8m for David Luiz when Cahill went on a free transfer?". He does have a point."

It is the final paragraph that is the topic of conversation today.

Has Cahill been a better signing for Palace than David Luiz was for Arsenal?

Well, let's delve into the stats.

For a start, the England international has helped the Eagles to two clean sheets in his six Premier League appearances so far, recording an impressive 5.2 clearances per game - Palace won four and drew one of those games.

The 33-year-old's experience has shone through in his performances for the south Londoners so far, where his reading of the play and composure on the ball have been the main eye-catching aspects.

He also didn't cost Palace a penny in terms of a transfer fee, strengthening his case in the 'Cahill vs Luiz' debate.

Now let's look at the Brazilian. As is often typical with him, David Luiz has made a few errors for the Gunners already in just seven Premier League appearances.

The 32-year-old gave away a penalty against Liverpool for a tug on Mohamed Salah's shirt, and was also woefully out of position for Christian Eriksen's opener in the north London derby.

His most recent performance offered signs of encouragement having scored the only goal in a 1-0 win over Bournemouth, but the negatives of his season outweigh the positives as of now.

In Cahill's case, it is very much the opposite. He has played a key role in helping Roy Hodgson's side sit 6th in the table - just one point behind Arsenal - and given the fact he was signed on a free transfer, it seems more than fair to adjudge him a better capture for Palace than Luiz was for Arsenal.

Maybe the north Londoners made the wrong choice.