The extra zoom might be handy, but only now and again I guess. As for the mic, again now and again it will be useful.
I am trying to get myself back into this as a hobby. I don't want to end up in a few months time wishing I had the option of an external mic and need to upgrade' as money is tight. I may even look to start doing some paid projects in the future (used to work as an editor/cam operator, but am long out of the loop).
The videos won't be for online viewing and so max image quality is one of my main requirements. But, if its barely noticeable difference......?
In an ideal world, I would go for the X900, but I just can't stretch my budget.