The SC has nothing to do with the amount of force needed to release out of the bindings. It changes the stiffness of the ski directly underfoot which translates to a softer or stiffer feel.
Here's my anecdotes... This is back when they were mounted on a set of softer skis. Approached a glazed over windslab/ice sheet and tried skiing it with the SC set to 1 and could not get an edge to set at all causing lots of washouts. Next run, I changed it to 3 and it was like being on ice skates, edgesets were sharp and crisp and I was able to carve turns in the ice. Yes, rela eastcoast type blue ice. In powder, if I left it on 3 the tips would have a tendancy to dive. On 1, I'd get float a lot easier.
Now that they are on stiffer skis than the old softies, the differences are nowhere near as dramatic, but still there.
Perhaps you've tended to use stiffer skis all along and that's why you couldn't notice any change in the feel. That or you were looking for changes in releasability and not flex.
Re: Pre-releases with Marker I've only had them come off when they were supposed to, BUT I don't do a lot of spinning.
Just an opinion from doing a lot of Marker bashing reading: I think that the Marker toepiece tends to actually finish releasing and not force the toe back onboard in those situations where the toe starts to come out due to torque that is close to releasing force. I think that's why jibbers and really agressive skiers who are bashing moguls that subject the ski/boot interface to a lot of shear forces tend to prefer other brands.
Anyway, that's my opinion (and it is of course worth what you paid for it.)