Frank,
I spoke with Bob Kallio at Midstates and he suggested going with a 12 to 14lb cap to allow the expansion tank to do its thing. Also hook your hose to the bottom of the puke tank to allow the system to suck the coolant back in.
In his opinion 460's that he has done always run at 195 and up to 220 on 90F days in traffic. His advise was that if you start to cool after getting out of traffic then you're OK to rise to 220. 230 is bad 240 you better shut it off.
I agree on the Expedition guage comment. I have one too and I know the guage doesn't really work, nor the
oil pressure.