Are European white truffles significantly superior in flavour to those from North America?
I think the truffles that are exported are of better quality on average than what you'll find on the european market. I've never tried the american ones consciously (they're not imported to Europe as far as I know).

You could also take into account that the fresher the truffles are the better the quality, so in theory it would be better to eat american truffles in the USA and european truffles in Europe.

Given the mind boggling price differences and the supposed high quality of the stuff found in the forests in Oregon, you're likely going to be well off picking the local stuff.