I don't have a Thundermax on my M8, but do have one on my 2015 SGS. I absolutely love it too. My recommendation is, if you plan on doing major motor work down the line then go with the TMAX, as you will be able to grow into it. If you're sticking with a stage 1 or 2, then go with the FP3. Your wallet will appreciate it. As for the o2 bungs, I believe V&H sets their pipes up to accept both stock and 18mm o2 sensors by using a reducer adapter. If you use the adapter the stock sensors will fit and if you remove the adapter the 18mm sensors will fit.
