Haven't seen any difference between the two. There is a major delay when FMnet refers to an invalid IP address. It takes FMP a long time to determine the address is invalid and either move to reference two in the list or display a "not found" message.
File: references are evaluated nearly instantly.
Thus a reference in this format:
fmnet:/<invalid IP address>/Filename
Will incur a major delay before attempting the secondary relative path address
fmnet:/<valid IP address>/Filename
Will almost instantly switch from an invalid relative path (first line) to attempt the second IP based reference.
Which method is preferred if all files are .fp7 and located in the same folder on the server?