Multi-Process or not 48 definitely feels a lot faster here! Looking forward to more...
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.
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).
This site is useful regarding the addon compatibility: http://arewee10syet.com/
Unfortunately I couldn't use my addons with it and together with the constant updates it was a no go for me.