This is actually a very complex question because the correct design pressure depends on how the adjoining piping system is designed and operated. PD pumps, of course, are a completely different question than centrifugal pumps.
An excellent paper discussing these issues is here:
Your question doesn't really make any sense, in fact it is meaningless- not unlike asking how long is a piece of string.
You need to fully describe the application if you want meaningfull input.
At the moment the only answer to your question is - "sufficient to overcome failure in operation".
It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)
In short, MOP is what the pump designer needs to design the internal part of the pump ( the pumping bit).
Max inlet pressure is what the pump designer needs to design the outer bit (the casing) and what class of inlet flange you need.
If there is a risk of back pressure through the pump with the inlet valves closed, then often the max inlet pressure can be the same as the max outlet pressure.
all depends on your system design and operation design.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
