I can't provide an apples to apples other than test drives. There was noticeable difference for me in corners and braking (less nose dive). Can't speak to the off-road difference because I've never driven a non-KDSS off road, but the science is there and that's good enough for me. I recently upgraded the suspension, 3" is the max you could go with KDSS I think, but that's the most you'd want to stretch other components anyway.
Glad to answer any question you might have, let me know.
Simply put though, I'm happy with my decision and would do it the same again.
This is on point with my experiences, and I know what you mean about forums in general.
For background I owned a 2013 trail edition with kdss lifted 2" on fox 2.5 coilovers, Radflo rear coils, and Fox performance series rear shocks. I currently drive a 2016 limited with radflo 2.5 coilovers and rear shocks and Dobinson's progressive rate rear coils (no kdss, xreas removed). Lift is around 2.5-3.5.
In stock form the trail edition behaved better on-road. The XREAS on the limited was smooth but there was more body roll than the stock trail edition in the corners. The difference was even more noticeable between an sr5 and a kdss trail, I almost wrote off a 4runner after first driving an sr5.
Offroad in stock form both were great. The limited came with 20 inch wheels from the factory so it's a little hard to compare. Any difference would be more than made up for by the rear locker and crawl control in the trail. Could a non-kdss trail edition get to the same place as a kdss-equipped trail, without a doubt yes.
In my experience the real magic of kdss is that it gives you the benefit of firm sway bars on-road, without the reduced articulation of firm sway bars off-road. I don't know what your background is but this is why jeeps often have disconnecting sway bars, let's them reduce body roll on-road and open up the articulation for offroad. The best of both worlds is a long-travel sway bar, ideally variable rate, a common aftermarket upgrade for solid axle rigs.
Toyota's kdss is somewhere in the between, it enhances the on-road performance of their current lineup without negatively impacting offroad performance. Does kdss increase suspension travel versus non-kdss? No. Suspension travel is the same on both. Does kdss allow more free-movement within its given wheel-travel off-road? Relative to heavy duty sway bars without any type of "kdss style" function yes. Does a kdss 4runner articulate more freely offroad than a standard 4runner? Maybe, as far as I know nobody has directly tested this. Practically speaking there's plenty of non-kdss 4runner and fjcruiser owners who can vouch for their vehicles ability to flex offroad. Here's a crummy video of my non-kdss flexing out:
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Some other considerations. If you plan to upgrade suspension, in my experience the felt-benefit of kdss on-road is reduced. The difference between my trail edition and limited, once lifted, was not huge. What really impacts handling is weight; winch bumpers, skid plates, rtt, etc. High quality coilovers and shocks will go a long way towards improving overall performance, especially if you keep the lift height minimal. If KDSS vehicles are not common in your area I'd probably inquire about maintenance. It has been known for kdss to start leaking at higher mileages and some special tools are required to service the system. It won't leave you stranded but it could cause a headache. KDSS has been on Lexus's longer than Toyota's so maybe see if there's a Lexus dealer near you who could service it. Lastly I'd consider what kind of roads you're driving, if you're on twisty mountain roads a lot kdss may be nice. You can't make a bad choice either way though.
Long story short, or if anybody doesn't want to bother with that, is from owning both I strongly recommend KDSS for those who are keeping their suspension stock, and no-KDSS for those who plan on modifying suspension. I'll repeat it again though, you can't make a bad choice and both sides are perfectly reasonable. Hope that helps.
