Just saw a NYTimes comment on the two terms, where they emphatically stated that "nerve-racking" is the only legitimate usage and that nerve-wracking is an utterly illegitimate usage—which is what you typically hear from British sources concerning any American spelling.
So, which sounds more natural to SOL authors?
Again, "racking" derives from the old Catholic torture of non-believers to force them to beg forgiveness—the same way they treated the ancient Vikings, by pouring boiling oil down down their throats until they 'accepted' Christ, at which point it was already too late.
That said, "racked" with pain makes more sense than "wracked" with pain does.
However, usage patterns how a different story, as "racking" is the traditional use (first used in 1882, while nerve-writing was only first used in 1900 and has been steading climbing every since.
The biggest argument though, is that the two are now common usage (despite what British dictionaries insist) but that nerve-wracking is viewed as being less commonly mistaken and less commonly misunderstood as well. Which seems pretty convincing for me.
Though the bigger concern, is how are readers likely to respond to the two spellings? Hence the usage question.
So, any visceral reaction to one spelling over the other?