I have just been given some 10w60 oil! 25 Litres in fact! However I am still not sure whether this oil should go into a 4200!
I have friends with older Ferrari's but............
Personally, if I did not have the 25lt, I would use the recommended 5w/40, however if I had 25lt of 10w/60, I would use that!
There are members on here that choose to use 10w/60 rather than 5w/40 with no reported issues.
Gixerboy told me at Brunty that he has run 10w60 in his QP for 40k miles without issues. Stops the tappety noise at start up apparently.
I believe the manufacturers philosophy is to use the thinnest oil you can without excessive wear as the reduced pumping losses increase power, but there can only be a few percentage points in it.