I forced e10s on 47, and it's still enabled in 48. In both I see random beachballs (OS X) hitting refresh in one tab and moving to another, and sometimes spinning wheels trying to navigate to a new tab.
I don't think there are any real performance improvements in 48 other than the improvement you'll get from restarting a long running process.
Have you tried with addons disabled? Your experience with E10s largely revolves around which addons you're using.
Some addons use compatibility shims with multi-process and this can significantly harm performance in some cases (even potentially making it worse than e10s disabled).
I don't think there are any real performance improvements in 48 other than the improvement you'll get from restarting a long running process.