In a situation where all 10 ports are used, but only 16 channels are needed (probably less), does it make any difference whether a single rtpMIDI session is used or all four? Think 10 mono synths and lots of CC and sysex while also time-critical notes are played.
If these were real MIDI cables, the 4 connection version would be better, as MIDI is serial. How closely is that mirrored by rtpMIDI? Is that "just" a virtual MIDI cable with all the consequences or is it done smarter, like sending data in a more pseudo-parallelized way, probably with a timestamp on top, so data can be received early and be sent to DIN at the correct time?