Actually, if you're going to assume some minimal amount of hits, look at how many can be bought, and stick with that. 3 hits = 12 dice - which is respectable for a non-combat skill, which generally isn't going to have any added dice easily available.
Of course, if you're presuming 4 initiative passes, it requires a 31 or more initiative - which you really have to concentrate on to get. On the other hand, four is by no means the most you can get. Presuming average enhanced initiative and average (not bought) hits, 8 x 8 = 64m/3s, or the Empire State Building's 443m - and since we're talking the Empire State Building, we really don't need to worry about ledges and handholds and stuff, the thing is chock full of them - in just under 7 seconds. Which is, granted, faster than the currently-fastest high-speed elevator (1200m/min) ... though that one's speed is deliberately restrained. It has to carry passengers, after all.