I do agree Sid/Biv, this is a good way to get a rough guesstimate of one's Skyline time. Your time equivalences are right on. But the only thing you have left out is the time for a first timer to make his/her way through the confusing maze of trails to MP! The first three times I tried, I got lost. So I guess it took me four weeks to make it to MP
And my first time on Skyline took me approximately a year and a half!
I always think that going halfway on Skyline, to 4500, is an excellent way to guage whether you are fit enough to do the whole thing. IMHO if you cannot do it in 3 and a half hours (without being utterly exhausted), your fitness level is not yet strong enough to take it to the top/tram. Provided it is not a superhot day (making a descent dangerous) this is a proven and safe way to prepare for a full Skyline. However annoying it is to make two long drives into town, instead of one, it's not nearly as annoying as having to be rescued off SKyline
Q: How many therapists does it take to screw in a light bulb? A: Only one, but the light bulb has to want to change ...