Tommicron,
I run 245/75R16 KM2's on my Pathfinder. It's an AU-delivered one, so has the 3.3L engine - we didn't get the bigger 3.5L version here. Hence, your performance might differ from mine slightly. However I also do a lot of towing with a trailer around the same weight as yours. I run a 2" suspension lift (not a SFD), but if anything, you should have more clearance that I've got. I'm also using the standard OEM wheels - if you do have a problem and want to avoid wheels spacers, you might be able to go an aftermarket wheel with more backspacing.
As stoic mentions above, I absolutely feel a big difference with the bigger tyres. Highway driving with the camper on the back is not the most effortless, let's say. The car will do 100kph, but it's working reasonably hard to do that. It much prefers to sit down on 90kph and you need to kick the OD out for any decent hill or incline. In third it pulls well, but revs higher than I'd like for highway traveling. Top speed with the camper on is just on 110kph, which means I need a LOOOOOONG stretch of overtaking lane to edge my way past any other traffic. That said, getting up to speed is reasonably straight-forward, it's just that it's not got much more puff past that magic 100kph mark.
Offroad, it's a similar story. I've just come back from a trip away with the camper. On one climb, I was down in first gear with my foot buried through the floor, and it was just chugging up the hill. We got there, and I was still in high-range, but it didn't have much more to give. Part of that is the dead weight of the trailer on the back, but I believe the taller tyres weren't helping.
However, I love the tyres and will be keeping them. The pros far outweigh the cons for me. They give good clearance, they're tough, and they'll climb anything. They're seriously that good. Aired down, they're even better. Around town they're easy to drive and you retain good acceleration for city driving. Braking is still good (could always be better, but has never caught me out). I'd have no hesitations putting them back on, but on the same hand I doubt I'd be game to put anything larger on.
Hope that helps.
Cheers,
Matt
Photo from Sunday, with everything packed up ready to start the 6hr drive home: