I have put 17's, 18's, & 19's on "S" class vehicles. for appearrance the 19's are show stoppers but, ride somewhat stiff. Careful driving can eliminate most of problems with wheel bending but, accidents do happen. 18's are very safe when you consider that the overall diameter of the tire for an S430 is 27". For the snow tire issue we are conducting our testing at this time and I will be posting some very attractive offers as well as the results.
Thanks, Luke