I don't know how much experience you have with the various Nscale engine manufacturers (you probably have a lot and know the following information already)...but I've found that each manufacturer performs differently on the tight curves. Due to space requirements, I can only use 9.75" as well and I've found that any Kato diesel including the 90MACs take the turns with no problems unless you hook MU diesels - then it's better to use a longer coupler shank on the lead engine (it's provided with each engine, therefore nothing extra to buy). Longer Atlas engines like SD60s and the like also have no problems. InterMountain's SD45s growl around the curves but take them fine. LifeLike Proto N and "regular" series engines work great - but most of the LifeLike diesels are the smaller 4-axle designs anyway. Athearn's long SD70 units run fine with no problems. Bachmann's longest engine, the Dash-9, growl taking the curves as well but don't have a problem - and the lone steam engine I run, the J-Class 4-8-4, takes the curves fine but not great. I know the overhang of the longer frame diesels is terribly unrealistic but on my layout that can't be helped...there's only 22.5" available to turn the trains around on my simple dog-bone layout. I laid flex track for the curves at first, but had more derailments than curved snap track, so I switched back to snap track for the curves and flex track for the straight-aways. That probably means I didn't keep the radius constant, so I fault my track laying abilities - not the trains. When I went back to using straight flex and snap track curves, I put a gentle curve in the end of the final flex track section to lead into the curves. This allows the longer passenger train consists a little less stress on the couplers before they hit the tight 9.75" curves. And on that thought...Kato passenger cars almost never uncouple on the curves but Con Cor cars frequently do with their "fixed" knuckle coupler. Bachmann passenger cars have rapido couplers and they stay coupled in all cases. Finally, track code, car weight, and wheel flange size certainly make a difference too. I have a few cars that are too light and will ride off the tracks when pulled between longer and heavier cars on the curves. (Adding weight to them is on my long list of things to do.) Hope this info helps.