OOOOOOH, tough call...... I have had 5 P3-28's in the past 3 years and were great motors. They have their querks but overall were pretty solid performers on the track for the money. The 528 is awesome but comes at a price. The OS looks decent as well, I haven't run them personally yet but the design was decent to work with and from what I hear they do run very strong, just don't know about the longevity yet, we will all find out soon enough. So in my opinion, I would get the Picco before the OS due to the price and past experience with that motor. All my Picco's have gone 8+ gallons with very little problems but my favorite is still the Rossi 528 due to its great design, reliablity, performance and long life. I had one of those 528's go over 12 gallons over 2 years and I just finally put a new one in just to have a fresh one on tap but the old one was still running decent when I sold it. I have a local guy getting a OS 28XZ and I will be modding that one and doing a report on it so I will post the before and afters of that project. I have no dought the OS will perform great, I just haven't seen how long they will go before getting tired.