If you don't drive the car hard, all the more reason avoid 10w60 - it will never get hot enough, to get thin enough, to flow where it needs to. The oil is just too thick to flow, which means the big ends will suffer.
As I said, unless there's a reason he recommended it, such as - high oil consumption, then you should use the specified oil, which is 10w40.
Both those mechanics are good as far as I know, but most mechanics don't understand oil - nor do i! lol But what I do know is that 'flow' is key. read the post i linked to above, it will explain better than i can.
That said, the JTS motor is spec'd for 10/60 because it uses oil. It has bad oil rings and high compression.
If I were you, assuming the engine doesnt have any underlying problems that would call for 10/60, change to a 10/40. This oil will get to the correct operating temp, will get there faster, and flow properly. Ideally, you want the journals to float on a cushion of oil - there should never be metal to metal contact..(except on idle) if the oil is too thick, you will never get that 'wedge' action.
I'd recommend Giancarlo from Marenello Pursang in Brunswick, they do have a pretty good understanding of this, but that doesn't mean they're the best - although I personally think they're great. They're also heavily involved in the Alfa club here too.
And if you feel like more reading - http://www.bobistheoilguy.com/motor-oil-101/
Also, 20w is WAAAAY too thick for cold starts.. you'll be scraping metal all over the place and the motor will take far too long to warm that oil up.. it must be a thinner cold viscosity. 10w is the number you want. Mind you, all oils are too thick at start up.. not much you can do about that - other than using an ester blend or ester base oil.
Hope this helps.