I stuck a 512GB SSD in my (8GB RAM) 2010 MBP maybe a year(?) ago. The general speed boost was incredible, of course, but the thing that made the biggest impression was definitely seeing several GB paged out, with little performance degredation.

I have had some weird experiences when pushing it hard, though. At one point when I got up to ~15-20GB swapped out, I encountered a kernel panic. I wasn't doing anything fundamentally weird, just loading a large amount of data into "RAM".

I should try it again and see what happens. I wonder how hard Apple stresses this functionality in QA?