I think I am qualified to answer having owned 3 FJ40's, 2 80 series and 2 100 series.
Both vehicles are very capable off road. I have taken my 100 every where I took my 80 series except the Rubicon trail. Not saying it couldn't go there, but being a bit wider and IFS would make it a bit harder. But every trail I went in Moab and Colorado with my 80 I have done in my 100. It comes down to the driver in off road capability, I have seen an outstanding driver take a stock vehicle places I wouldn't take a built truck
As far as IFS, except for the Rubicon, my daughter Rachel could follow my 80 with a 4" lift on 35's everywhere I went with her 99 IFS 4runner on 33's. But since I taught her to wheel before you could drive on the street, she is a better driver than most men in my club.
My 80 was supercharged and tended to run hot a lot and still couldn't go above 50 towing my Kimberley Kamper going East up Vail pass. Everywhere else was fine so not a huge deal.
My 100 series rubs cool and I can tow the same Kamper going 65-70 on the same pass. I always liked being able to put Burritos in foil in my engine bay in my 80 and having piping hot food for lunch. My 100 series engine bay never gets hot and I get luke warm food.
So, If you plan on doing heavy wheeling with big rocks or a hard trail like the Rubicon, the 80 series is better. For expedition wheeling they are equivalent in capability. Then you have to decide if you want to spend the extra money for the more powerful engine and a few extra comfort features.
If you want to build your truck for 35's or more, then the 80 series is superior.
If you plan on towing a camper on your expedition runs and have a lot of Mtn passes to get there, the 100 series is superior
Both are great vehicles. Remember, both are Landcruisers and share much of the same engineering concepts and quality
Some will put a 100 series engine into an 80 giving it more power. Some have put a solid front axle on a 100 series improving its off road capability and enabling larger lifts. Both are expensive options but allow you to take the unique improved capability of one vehicle and add it to the other
AS far as the previous post. I have shoes with grease and dirt I still wear, I do have a Tommy Bahama shirt, I have never broken 100 on 18 holes of golf. I do fill out the arms of my Polo short. I prefer Beer over Tea, probably why I have never broken 100 on a gold course
What you wheel really comes down to personal preference. What works for one doesn't work for others. You should try and drive both and see what you prefer