correct, been there done that, negligable bump steer, i calculated it to be about 2mm toe change over the entire shock stroke, from full bump to full rebound. i bet the 86 gear has this as well anyway. i should do some measurements.
so i thought i would explain my experiences with the s13 gear and my new ae86 gear.
old setup (had it for 4yrs), ca18 brakes, base adjustable and adjustable damping coilovers, standard mastercylinder.
pros: cheapish, in a ke70 at least. epic lock out of the box.
cons: weird steering compared to the 86 gear,steering tends to tighten up the more lock you wind on (i didnt notice it untill i drove with proper 86 stuff). s13 coilovers that are suitable for grip in light cars are VERY difficult to find. went through ~3 sets trying to find different ones, bought a few different spring rates along the way. i ended up with an ok setup, but it was still a little stiff.
new setup: brand new everything, jap 86 calipers (rebuilt), vented discs, 40mm rca, kyb excel g inserts, 6kg springs (welded sleeve for coilovers) new brake lines, standard non-powersteering arms,
conss: bloody expensive. (though that could be because i bought everything brand new)
pros: steering is much more "normal" compared to s13 stuff, the effort required to turn from lock to lock is the same. a normal amount of track (though R31 arms have been sucessful in reducing track in s13 gear). its a much better setup compared to my s13 gear (though read on)
so i have used both a "complete" ae86 setup (RCAs, jap brakes, coilovers yada yada) as well as a proper s13 setup, in the same car, and have used them back to back, so i belive i can make some pretty reasonable comparisons between them both.
my oppinion is that both setups could be made to work well, its fairly obvios that the ae86 stuff works well straight out of the box since its based on standard equipment. but i still belive that the s13 gear could be made to work, but i did not like the "twitchyness" of the s13 gear. maybe if you bought some funky custom nuckels that reduced the steering speed of the s13 gear it might work well. though somepeople might like the REALLY quick steering. since driving around with standard 86 steering arms, although you do have to steer more, i find it easier to control, though i have not taken it through the twisty roads where the fast steering really was quite good. im a little hesitant to get the powersteering arms, anyone want to take me for a spin in a ke70/ae86 with power steering arms?
to me the main draw back of the s13 gear was the difficulty in finding decent coilovers suited to grip (soft dampers that suit soft springs). its easy to find damper/spring combos that suit drifting but i was after more grip and unless i either bought brand new coilovers or had a pair revalved to suit it was difficult to find a good setup. and of course you can get new coilovers or get them revalved, but its not cheap, and the main calling card to s13 gear is its apparent cheapness.
so to all the guys out there who plain out say "s13 gear is crap" i can say that is in fact not crap, it just needs a bit of work and planning to work well.