I ran Piccos for a few years in multi (submerged drive), 21 on a gearbox and 67 direct. The main problem I had was with the 67, and the big end rotating.
Even though I chamfered the oil holes, polished the crank pin and frequently checked for blockages, every now and then the PB big end would rotate slightly, putting the oil holes out of line - then bang! Another banana shaped conrod! That wouldn't have been so bad but it usually left a square section of the bottom of the liner sticking out, which I had to grind away to get the liner out - thus new piston and liner required also
Thinking that things MUST have changed by now, I bought a new Picco 67 and ran it last year. I think it was the second race when - you've guessed - con rod gone!
Now before you think that I'm an idiot who doesn't look after his engines (not that you would think that of course .....) I ran a very fast Serpent (Novarossi) for 5 years, my CMB 21LS has done 4 years, my CMB 45 has done 4 years, and my CMB 80 has 2 years running! The last time I sent the 45 for a bottom end service (after 2 yrs running), Ian only replaced the needles as the rest was fine.
Maybe I'm just unlucky but I've not had anywhere near that longevity from Picco or (in my early days) OPS.
I may eventually run the rebuilt Picco 67, but it will only be when I've run out of other options.
Every make has it's followers so this is just my opinion.
BTW Roy, ironically, I like the Picco carbs which I can get to throttle better than CMB ones - which I think are REALLY naff!
Danny