Posted By:
Joe D.I have shipped items that were worth about half that (2500).
Overnight Insured came to about $10 or so more than Registered Mail would have been.
I can't say exactly without looking it up... but I bet the difference between overnight-insured and registered mail insured for a $5000 package is no more than $25 (now I have to go check it out on the post office website 
)
Realize that the Post Office charges about $15 to ship something overnight.
Whether you insure it through the registered mail process or through the overnight insurance.... in both cases you have to buy insurance based on the dollar amount.