Dear PNW
I am no computer expert and have not been able to get my FSX boxed back onto my PC since uninstalling it (when I rashly thought FSX: SE was all I needed) so a side-by-side comparison is not something I can supply with validity.
However, when I first installed FSX SE I just noticed that there was no stutter whatsoever and the sliders seemed to all start at max. It was quite something.
Someone made a valid comment that new installs always feel like that, but even adjusted for that 'new install' effect I never recall FSX Boxed being so smooth from the get-go.
It surely must be something to do with the fact that it's been designed to work properly with Windows 8.1 and there are some technical improvements too. Be warned, there is some fierce debate going on about this issue.
So I can only give a subjective opinion, I am no PC programmer just an enthusiast.
Right now I'm in the position of FSX:SE installed, FSX Boxed uninstalled and not re-installable. So I either wait for ORBX to produce a patch/app or I do a clean Windows reinstall, then install FSX Boxed then FSX SE.
The latter option is probably somewhat excessive and ulcer-inducing when I have so many demands on my time!!
My sense is that most people are running dual installations and will take a view when ORBX produce a patch/app. If that app works well (and I'm sure it will) my suspicion is that FSX:SE will be the one to choose if indeed a choice has to be made (personally I need the hard disk space).
People will yell at me for that statement but there is a cleanness to the new version that makes it preferable in my view. And there is the promise of future updates as well.