Not sure of your timetable for this ride but frame material is not as important as bike fit as long as the frame builder and design is good. Commuting 10 miles on the saddle you have will feel very different at 75 miles for your 2 day 150 mile ride. Start riding longer distance on what you have to see how your body is reacting...adjust as necessary. If there are many hills within the 150 miles I would start doing some hill repeats during the week to add miles. Have fun.....