I have been on a 56 traditional almost since I started riding some 10 years ago on a 11cm stem.
I have riden Colnagos on sizes 57,56,55 and 52s.
I find myself the best on the 56 traditional or 52s ( same virtual dimensions ) on a 12cm stem.
My EP is a 52s, this was my first Colnago. I bought it from a guy with very similar measurements as me, only he is fatter and older. He bought the bike for the looks and set it up with a high handlebars and short stem.
He sold it because he dindn't like the way the bike rode and felt. he sold it to buy an Specialized Roubaix ( if that is a hint )
At that time I was riding a Bianchi 928SL in size 57 that has same virtual dimensions as a 56 traditional on a 11cm stem.
I tried the EP as it was setup and also didn't like it nor found an improvement compared to the Bianchi.
Then I started looking for other Colnagos and tried one in 57 with a 11cm stem with low handlebars and it was good.
Finally I bought my Extreme C on a 56 Freuler ( the frame is like a 54 with a longer head tube ) this Extreme C had the steerer tube cut very short and handlebars are very low, it has a 11cm stem ( Cinelli Ram ) but the TT is 55 cm.
I had put for sale the EP 52s and bought a C-40 in size 55 this one has a 54.5cm TT, the EP 52s has a 55cm virtual TT.
well, I set up the C-40 as close as possible to the Extreme C and experimented with 11, 12 and 13mm stem and high and low handlebars. The bike felt, rode, climbed and descended beautifully, probably the best would be to find a 12.5cm stem though.
So then I went back to the EP, set the bars as low as it was possible and a 12cm stem. ( I think I could go to 13cm and it would be better but helas my handlebars are also Cinelli Rams, maybe i would look for another Cinelli RAM in 12 for the Extreme C )
Now the EP was a completely different bike. The handling, feel and ride is much much better than what it was before with the handlebars 2cm higher and 2cm shorter stem.
Needless to say, my Bianchi 928SL feels and handles "big" now, not as agile on and off the saddle as the Colnagos, It is now for sale.
keep in mind the Colnagos head tubes are longer due to the non-integrated headset.
So, I am no expert, but I find those 2 articles I posted make a lot of sense.