The Rival and The Icon use two vary diffrent Shells ,so no they will not fit the same. The Rival has an over all wide fit. The Icon has a wide toe box yet the fit at mid foot and the heal pocket aren't all that wide. The only way you can ever tell if a Boot is going to fit is to try it on and ski in that Boot. I understand about needing to save a few bucks. However buying used boots is always going to be a gamble. Your best bet is to go to a local Boot fitter that has been recommended to or a ski shop you know and trust. to save on gear,buy used Skis and even used Bindings, but not used boots! A good fitting boot is worth every dime you spend on them. Your boots are no place to skimp. Painful feet will ruin a day of skiing. Sloppy ill fitting boots could lead to an injury that could also ruin a day of skiing or the rest of the season. Look if you need to save some cash. I have seen some of last seasons boots on sale in some of the Big Box Retailers like Garts Sports. You would be better off buying boots from them then used. At least with them you can return the boots if they aren't right. Ok end of lecture. Ok Your not convinced you still think you can get a good fitting pair od used ski boots. If your going to be shopping on ebay be sure that you can return the boots if they don't fit. Keep in mind that those return shipping bills will start adding up.