W10M has wrecked my battery on every device I've put it on. Most recently the 1020, which was taken from a day of battery life to about 6 hours, and less than 2 hours with that Skype Messaging Beta (all based on casual operation: send a couple messages, snap a couple pictures, check FB every now and then... no games, streaming vid out anything).
With that said though, it has been VERY SMOOTH... haven't had it on a 512MB'er since 102xx on the 635, but it's been real damn smooth on everything I put it on.