I think the easiest way to understand it is that Suzuki designed the original Sidekick with a certain power to weight ratio in mind, then as they started making the vehicles larger and heavier, they would either modify gear ratios by adding gears to the transmission or by running lower or higher ratios in the diffs, or started producing engines with more power (started with the 1.6 8v, then upped to 1.6 16v, then the 1.8, then 2.0, then 2.5, then 2.7). They only added beef to the driveline components when absolutely necessary to keep the power to weight ratio good, as well as keep the power to durability ratio the same. I wouldn't say that an XL7 or GV with a 185 hp V6 and steel diff is any more durable than a Sidekick with an aluminum diff and an 85 hp hamster wheel. The CV's are probably the weak link on the models with the steel diffs because although they are *slightly* larger, it's hard to tell the difference without comparing the two side by side.
I think you'd be wasting your time trying to run 35" tires on Zuki IFS. The components just aren't designed for that size of tire. Even 31's are hard on these rigs...35's would just be expensive and frustrating!