Rob,
What I'm doing when I load a new sample is usually to load it in 16 bit and base on the sample producers memory consumption judge if I can load all the ranks.
Once loaded, I check my free memory. Usually I will play for a while with that setup. Since you can have 2 HW configs (regular and sequencer), the next time I have some free time (going out to do some shopping, have dinner, going to bed) I load on the other HW a more agressive configuration than my first load; if I successed, this version becomes my new "base version" and so on.
That way I only have to wait for the first "long load" and always have a fast playable fast loading version available and can take my time to work on a more complete one when not in the rush to play.
François