I spoke with a few tire shops today and got an email response from Tire Rack....
Tire shops - none recommended switching, they said it would cause the obvious speedometer issues, but also added that it might cause safety issues with the bigger tire.
Tire Rack email...the guy advised that the only 18" tire size in his database would be 235/55/18, then he recommended the Goodyear Assurance ComfortTred.
I think I'm gonna go with Dueler H/L Alenza's.