Probably has more to due with the yeast strain then. I'm using all English strains, almost all rated at least 'high' for flocculation. I also get a really good vortex going in the starter. Basically, I make sure it's centered and then get it spinning as fast as possible. When the bar starts clanking around, and I can't quiet it down by shifting the flask, I back off a little. Except for old yeast (6+ months old) I've never had a starter not going really good in under 18-24 hours. If I'm not using fermcap in the starter, then I get a really good amount of foam on top.
For how fast it settings/compacts in the fridge, it really does matter on the yeast. A strain rated at least 'high' in flocculation will be done/settled in 24 hours (possibly less). Something rated lower than that will take longer. I had a yeast rated medium that took an extra 12-24 hours to get to the level I like.
I buy just one smack pack per batch. With that one pack, I can use a starter to get me the cell count needed.
I would advise looking at the thread/article on freezing yeast. Get an extra smack pack of a strain you use often, step it up a couple of times, and then freeze the slurry (after treating it with a glycerine solution) for use later. I wouldn't do that with a yeast harvest, since you have less way to know what's trub and what's actual yeast. At least that's the case for me (color blind). I'm planning on taking one of the vials out (soon), making a couple of starter steps from it and using that in a batch. I'm thinking of using one of the vials that has a lower yeast layer in it, so that I have less risk.
Besides, stepping it up a few times should give me what I need for the batch I'll be using it in. I MIGHT try to harvest the cake from that.