'BeeLine' pretty much nailed it. I think the poll is a little erroneous because the two -- sight distance & corner entry speed -- are directly linked. Quoting MSF, "From your approach speed, slow to a suitable entry speed." That's based on many things, like: ability (both bike's and rider's), visual input (which includes sight distance), familiarity/unfamiliarity with the road, level of risk acceptance.
Ultimately, I think, most road users may exceed, a little, their sight distance on mountain roads (hills and curves) and operate on a certain level of faith (and the hwy. depts. relative corner speed info signs) to successfully ride/drive at a speed that's comfortable enough (safety-wise) yet not so slow as to impede the flow of traffic.
MSF also says (concerning 'corner entry speed'), "Continue to slow until you see the (corner) exit." That certainly is the 'safe & sane' advice -- but may lack some real-world practicality....?