You could consider Goodyear Assurance Comfortred tires. The P205/55R16 size is "H" speed rated and they are getting decent reviews for ride comfort at tirerack.com.......... I put a set of these on my 1995 850 and was amazed at the improvement in the ride. (I am not an aggressive driver). Goodyear advertises that you can return them within 30 days if you are not satisfied, but you have to pick another tire to replace them with - not a money back guarantee. I've heard that the T5 suspension is pretty stiff, but they should certianly be significantly softer than the MXV4's you are riding on now. This tire will probably give you the softest ride of any "H" speed rated tire.
They are priced around $100 each ($92 at tirerack.com)

http://www.goodyeartires.com/goodyeartireselector/display_tire.jsp?prodline=Assurance+ComforTred&mrktarea=Passenger&size=205%2F55R16&sidewall=VSB