I made some estimations based on the design renderings and the 5.7" screen size. You can find it here: Size comparison to other phones
Also the librem 5 will be ~14mm thick which is 3mm more than the Fairphone2.
And i think the librem 5 will have a metal back which tends to be heavier than plastic.
From my point of view the librem 5 will be a big heavy phablet and that is for me to much of a compromise to do the jump form my iphone 5 to the L5.
But i think that is the thing with libre and privacy, often it still is a big compromise, which not so many people are willing to do, but purism is doing really great in making it less and less an issue, while the big companies are increasing the pressure to go away form them.
It’s just the question how annoyed you are already and how much you are willing to compromise to escape. 