Greetings,
I use 1/0 pins, and have for a number of years after hearing Chris Robinson describe their use after he had to replace a number of soundboards he had installed that turned out to have been assembled with faulty glue. He said that he replaced the pinblocks in these warranty re-rebuilds since he wasn't going to send out pianos with 3/0 pins. His view was that if there was ever a problem with the blocks, (I never heard of any), he could pin them one size up and voila! he was back to conventional.
I discount the plate bushings as a contributor to any pin support, as their longitudinal grain orientation makes them susceptible to crush from the get-go and after a year or so, I don't notice that they make any differnce to either torque or flag-poling, I may be wrong on that, but a number of Chickerings I used them in showed no effect when I noticed a pin here and there had not been centered in the drilling and there was a small gap on the distal side of the pin. With the obvious lack of support, those pins still felt and tuned like the others.
I use Bolduc blocks, and I drill them out of the piano. I go first with a .200" bit and then make the final dimension with a .250" bit. This idea came from Ron Nossaman, and it totally obviates any concern about heat or 'glazing'. It also allows the bit to cut a more consistent hole, as it is not being 'steered' by that center point on the nose of the bit, but, rather, is just removing .o25" of wood around the circumference of the pilot hole. It can even side-step the slight tolerance I have in an older drill press. No worry about feed speed affecting the actual size of the hole, nor worry about chips or a hot bit. This gives me a consistent 125 in/lbs of pin torque that drops to around 115 after a few years, which is where I like to tune. Of late, I have taken to drilling the top two octaves with a .253" bit to leave a torque closer to 105-110, as that is more than enough and makes tuning stability easier to achieve. For others that may use other blocks, I think you could drill them for the 1/0 pins with the same undersize you use for 3/0, whatever that may be.
I dimple the top of the block with a 5/8" bit,( or whatever size is a snug fit in the holes of the webbing) through the plate, to get my location. Usually about 1/16" deep, which makes it easy for me to eyeball the pilot hole's centering. After the pilots are drilled I will put the block back under the plate and examine how accurate I was, (I ain't perfect). Any that appear un'centered get a red dot on the wide side and when I am drilling the final hole, I can easily see the concentricity of the larger hole as soon as the bit touches the rim of the pilot hole. I have that .025" margin of error to leave the final hole closer to the ideal centering.
I haven't tested the bend strength differences between a 1/0 and 2/0 pin, but I think it is negligible. I was told by a factory worker that the 2/0 pins were preferable as they were less like to be bent in high speed, powered production line stringing where pneumatic equipment was driving the pins. I got a hammer and time, so that isn't a consideration. The smaller pin leaves a little more room in those older pianos that have webbing holes that are almost the size of a 3/0 pin. I have put these in the bottom of larger pianos, and they hold torque as well as anything else I have used. I use the longest pin I can for durability, and leave coils maybe 2- 3mm above the plate.
This has been my experience, but one stand-alone example isn't the final word, so am open to other suggestions. I have been through my Falconwood phase,(extremely sensitive to drilling protocols), but the Bolduc/blue 1/0 combination installed as described above has worked 100% of the time for what I am looking for.
Regards,