I did a six-flight trip once (one overnight stay involved due to final flight being on an EAS leg), with 56 hours, I think, of traveling. Could have pushed it to 7 if I hadn't already been at the one international airport in the origin country, and I could have cut the EAS leg out if my family had driven 2 to 4 hours each way to be able to get me at a larger airport. Friend of mine did a trip that required, I think, 9 flights once. (from somewhere in the Alaskan bush to BDO)
I think anytime I have to flight with multiple flights over 4 hours is brutal. I've done ATL-DXB direct flights with a flight on both sides of that, and I've done ORD-DXB with a stop at LHR or FRA with an additional flight on both sides. I'd much rather have one 15 hour flight than two eight hours. On the 15 hour you can sleep some, maybe get a little ahead of jetlag if your timing lines up well. On the eight hour, you just get abbreviated naps, no sleep cycle, and you might think, oh, but you can get out and stretch your legs, usually what ends up happening is you get stuck going through customs somewhere and stand in line forever, then cram yourself into another plane. Give me one flight.
My worst was 42 hours (with an 8 month old baby) going from the US to New Zealand via Australia. It included an unscheduled 10 hours in SYD due to Virgin Australia not understanding visa regulations for New Zealand. VA tried to have us sent back to the US and Australian customs ended up giving the airline a five figure fine due to how long they delayed us. The thought of another 15 hour flight with a baby after 38 hours was not a happy one...
I think anytime I have to flight with multiple flights over 4 hours is brutal. I've done ATL-DXB direct flights with a flight on both sides of that, and I've done ORD-DXB with a stop at LHR or FRA with an additional flight on both sides. I'd much rather have one 15 hour flight than two eight hours. On the 15 hour you can sleep some, maybe get a little ahead of jetlag if your timing lines up well. On the eight hour, you just get abbreviated naps, no sleep cycle, and you might think, oh, but you can get out and stretch your legs, usually what ends up happening is you get stuck going through customs somewhere and stand in line forever, then cram yourself into another plane. Give me one flight.