#1 - You'll probably incur a small hit but the authority is so closely matched between pages I don't see it as a massive problem (are the .com pages ranking btw?)
#2 - Adding a 301 to a page will pass most of the authority/link juice but not all. The 'time taken' can depend on the next time the page is crawled and indexed and/or how often the page is crawled. Hard to give a definite I'm afraid!
On a side note - Other members will say if you're ranking then why change what you've currently got? That's fine - but in my opinion you should 'future-proof' as much as you can and having the www. version is jut best practice.
DD

