Dayton Wires 17 x 8 for my 2002 xk8
 

I recently came into possession of a set of !7" Dayton's. My 2002 xk8 currently rolls on staggered 18" impellers with peeling chrome. Before I ship them off to Dayton for a refurb, I want to make sure I know what I'm into. I checked the speedo calculator here: here: It shows a 255/50-17 has essentially the same circumference as my 18's so I should have no problems? These came from a 99 xk8 so there should be no fitment issues? Dayton wants $1100 for the refurb which sounds reasonable, but I'm having trouble pulling the trigger.

Thoughts?