Adjudication? Sorry GM and XR, you're overruled. There's no stopping anyone doing long races for their choices - 20-lap races are a staple of Avalon, and I think Luxoflux specialised in them - he won the Avalon Cup after all.

Given that you set the challenge and nutcase accepted it, the only way you can back out is to accept a 0/7 loss. I say just go for it, and work on your endurance skills.