Sample is sample. It doesn't matter if your Performances live in the Library or User area - samples are going to consume your 1GB of Waveform memory.

The reason why a Samplerobot version could take up less space is that you can sample less velocity layers or less regions with a single sample or less quality sample (depends on the bits and rate of the original if you can do this or not). There are lots of dimensions you can reduce when you refactor and end up with something smaller. Smaller, but not zero.

When sampling, you should probably turn off the key-off noise element. You need to redo keyoff with samplerobot yourself. I would just use the CFX key-off such that no more sample memory is needed. I doubt there's any real difference when playing.

I know this is an old thread, but thought I'd share something I did in case it helps anybody else:

For me the main value in the organimation set isn't the samples (which are relatively similar to the stock ones in my view), but the rotary FX and preset programming.

So to save space, I took a handful of the patches I needed most and switched them over to use the stock modx samples instead, so I could delete the 3rd party waveforms - well most of them - from memory there was one which blended 2 drawbars which I kept as I couldnt easily recreate it. By balancing the volumes and particularly the volume tracking for each waveform across the key range I got close enough for my live purposes, and so could delete the main library to free up space.