We race Marathon Whitewater Jet boats, 366 ci SBC with larger than normal main and journal clearances (.029-.030 in.) because of the extreme and numerous shock loading the engines endure. We race for long periods of time at a steady WOT and the motor may see over 400-500 incidences of shock loading as the boat leaves and returns to the water per weekend. It is not unusual for guys to turn bearings or break the balancers of the front of their cranks if their not careful. We've been using Joe Gibbs XP3 (10w30) race oil and have noticed some unusual bearing wear as this oil is designed for clearances in around .027 or less, so we're thinking about changing to a heavier grade. We've also noticed much more corrosion in the engine at the end of the year than we would like to see as Joe Gibbs has no corrosion inhibitors in their Race oils. So, we're looking for a heavier Extreme duty oil and are considering Mobil 1 HP 15W50, Amsoil RD50 Race oil 15W50 or Joe Gibbs XP6 15W50 (and learn to live with the corrosion issues). We're hesitant to use Mobil 1 15W50 high performance as it seems like a generic high performance oil not a purpose designed Race oil and we have no first hand information on Amsoil at all. Our engines cost about $40,000 each so we like to get as much verifiable and objective information on what we need and use the best products we can.......within reason. I would like to hear your comments and recommendations. If you do recommend to use or not use a specific oil, please provide details to support your opinion. Thanks in advance.