There's a billion threads about this.
I know you didnt ask about this - but 265/65/18 fits with minor work. Same with 285/60/18. Bigger takes more work and doesn't make much sense IMO - why add all the unsprung weight? Also if you have a suspension fault on trail you'll be stuck.
E load rating or not will set off a major flamewar around here. E load rating specifically does NOT mean that a tire will be more puncture resistant - I just verified this with an actual tire engineer at Goodyear and I'm working on talking to one of their lead designers to understand exactly how to interpret these ratings with publicly available info to get the best tire for the job without running a 60lb tire designed for an F-350 when we never run 80psi.
Personally I run 265/65/18 SL114 rated Duratracs. I'm sure Jwest will chime in to say that anything without an E-load rating will puncture immediately. This hasn't been my experience, but I will not say that he is wrong (for now anyway) until I've spoken more to the guys at Goodyear/BFG/etc. Pirate4x4 tends to err on the side of running the lowest load rated tire for your rig, for what it's worth.
Possibly a bit of overgeneralizing and semantics but the point is that an SL is not as good of an overall choice than something built to handle more.
An SL tire for off road use under a 6000 lb vehicle would probably be considered a very unwise choice by every professional in the 4x4 world. Doesn't matter what you think you've seen on Pirate4x4 as some people just use what they have, are cheap, or have much lighter vehicles trailered to a trail, etc.
Maybe you just missed the primary point that while an E load is not 100% necessary, D or C load is often not available in a size or model, thus one must go with E. It is my understanding that an SL is for cars on nice terrain.
Referencing the 80psi is pointless when the F350 doesn't use 80 psi either, unless under a high load situation. The tire's max load at psi doesn't mean it is only designed to be used at that range. KO2 E load tires are used for competition but not at 80 psi ....
I never said the BS line about "puncture immediately" or anything like it. The sidewall however, is of course more vulnerable, especially when in off-angle situations where 90% of the weight is on 2 tires. You don't have to care but it's just a fact that the stronger tire will hold up to more abuse on average.
Why don't you go back and ask the engineers which tire they'd put on their 6000 lb vehicle for real off-roading beyond forest roads. Maybe even like a 3000 mile trip that is highway, gravel, and a few black rated colorado mountain passes. Unless they're going in a Subaru, it's unlikely they'd choose an SL.
To me it's all about reducing risk and tires are one area where it's easy to do so. Those of us with no less than 7000 lbs are not going to be using an SL tire for anything and no industry professional would for off road use. Sure it weighs a little more, so go with a narrower one or a smaller one or just slow down.