I'm a medical professional and I specialize in the respiratory system. I'm very familiar with OSA and its treatment. Your correct, large neck girth is a correlative factor to OSA. Dental devises are kind of an issue for me because: 1) OSA is a process that effects more than just the oropharynx (the back of the throat where the nasal passage meets with the oral passage), the dental device only effects the oropharynx by shifting the jaw forward and creating additional space for air to flow uninterrupted by tissue that collapses which causes the obstruction. 2) the dental device has been shown to cause dental drift, i.e. Your upper and lower teeth will shift like your wearing braces and have to be resized every few years due to this drift and the associated lose of efficacy over time. A CPAP or BIPAP device is actually significantly better as a for of treatment due to the fact that the positive pressure will splint the entire upper airway and it will not cause the deformation of your teeth. On a side note a CPAP will also improve you oxygenation while you sleep by as much as 50%. The additional positive pressure it provides will increase your FRC (functional residual capacity) allowing you to sue more of your lung tissue than normally possible. Being that muscle recovery hinges on oxygenation it would actually be beneficial for improving upon your gym goals. Ultimately the choice is your but I figured I would touch lightly in the subject lol.