I can second this conclusion, but it took us 4 years to put the same solution in place. I had a thread called "Timed breather, what is the actual timing". Our reconditioners had also advised that the old pistons were ok, with only a hone to the bores. To compensate I went the Total Seal Gapless rings way, but I think that just exacerbated the crankcase pressure. So, we were distracted from the underlying excessive-blowby situation. I lengthened the breather valve holes, and narrowed the valve clearances by inserting K-liners. These weren't bad mods. The last time I had oil over the back wheel it turned out pressure hadn't pushed out the drive side oil seal (like it had in the past). But there was too much oil coming out of (where it should, in such a case) - the breather exit pipe, and high consumption. My oil was always black, though - indicating blowby contamination.
My engineer had detected an imperfect part of the bore (caused by rust from 30 years being left), but he was more insistent on new "decent" pistons. I believe the only ones up to the quality he was after are IMD. Adrian Wright, the proprietor, dealt with me personally, with all the specs. The rings that go with them are a big part of the advantage. They are deeper and narrower, and come with their own 3-piece oil ring. He said "you don't gap them" and I didn't - because I couldn't get them out. My compression isn't as low as the pistons are rated because there was barrel and head skimming involved (some of it unavoidable), in my rebuild. It's probably about 8.1:1, lower than the 8.5:1 my old domed pistons were rated at. It kicks over easier. I did the "stationery" running in procedure that Klaus described. From my first ride the bike was much smoother-running and more powerful than before. The plug colour is light brown - from idle through to full throttle.