i take stairs on my xc bike w/2.2 tires w/e i don't weigh alot
anyway yeah you don't want a dh bike more of an all mtn or and inbetween from the am and a xc, the prophet is really good but i would def step up to the 3 over the 4 so worth it btw they don't make the a prophet 8 anymore, they changed up the numbers and now a 4 is the lowest
i would also really look at teh rush depending on your weight, full suspension with a little less travel than the prophet, but way way stiffer on climbs ect, and if its your first mtn bike (you said you were a roadie) i doubt you will be good enough to need a prophet, but once again weight is a factor, if you like me and you weigh 145lbs you basically don't have to worry, but if youare like in the 180 range the prophet would suit you better