ANY correlation on the UW vs. Step score issue is rough at best. Don't hang your hat on it.
That said: RapplixGmed here on SDN looked into exactly what you're talking about, and then published some stats on what he found. You'll find that here.
Anecdotally: there's the (UW)*2.4+84 thing, and the "65%-70% should be ~240 territory" thing. fwiw.