Wheelbase dimensions or any singular dimension will probably not address your desending issues as much as specifically addressing what is your issue in descending. Who knows maybe you need different bar/ brake lever position or posture. I did most of touring on raod bikes, sport tour and standard road racing bikes. 50 yrs later I’m on a ClemSmithJr off road most of the time and love it. Descending, ascending, gliding, floating, crasing into a cartwheeling heap aren’t about an extra inch in wheelbase.