Yeah, the difference would only appear if you'd run out of memory. That's not totally unheard of, at least if you like to use Ram Disk a lot. It clearly depends on the stuff you do.
Not knowing anything about the underlying architecture of MorphOS, I wasn't sure if adding the extra ram would increase the performance any. On OS X trying to use the system with 256 is a waste of time, even though it's not swapping. I'd never even consider using OS X without at least 1 GiB of ram. Don't some of these operating system kernels use the extra ram available for caches and/or use different algorithms for things where the extra memory available is more optimal? And I'm not complaining either, the performance of MorphOS is excellent. It boots in seconds, OWB loads in like a second and plays youtube videos on the machine without a hitch. Got the SDK issue ironed out so all the familiar tools are available. I'm a happy guy, I've been using the machine a lot.
One thing I've noticed though, if the screen resolution is high enough, when a window get stretched out after a certain length, it starts to lag on the stretch operation. What's the cause of that?