Shadorne,
The distortion occurs first at the very first big climax at about 3or 4 minutes into the first section. Ditto the next big blowout a couple of minutes later. If you get through the first movement without distortion, you have a better copy than mine.
My speakers are quite comfortable at 104db. This is a peak averaged reading, of course, and covers all frequencies from roughly 50hz-10khz. I have Shahinian Hawks and one of the many amazing things about them is how loud they can play without distortion or change in character.