I have a 2015 1.1 base model. I just tested all of those sites and it was lightning fast. Nothing was slow or stuttered and my CPU usage was only at 12 percent. I have the weakest of all of the 2015/2016 MacBooks and I've never ran into anything that slows me down. Now if I have 10 programs open and try to do something real quick, sometimes it will pause for a second, but that happened on my 2015 retina MBP too. Everyday I still get surprised by what this little machine can handle.
Obviously there are power users who could not get by on a MacBook but for 90 percent of users, it's the perfect machine. When the MB first came out, many tech snob reviewers claimed how weak it was because in their eyes, anything that can't edit 4k video in a nanosecond is slow or weak. It got a reputation for being incapable of doing the most basic tasks.
My normal workload includes Safari with 5-10 tabs, iTunes always playing music, at least 2 or 3 pdf documents open in preview, 1 or 2 MS Word documents, Mail, iMessage, Chrome with a couple of tabs, Calendar, Notes, and I am usually running Visual Studio in Windows 10 via Virtual Box. Even with 3gb of my 8gb of ram allocated to Virtual Box, I rarely have any issue on the Mac side. If I don't have Virtual Box running, then I can do even more.
I have noticed no difference between this workload on a 13 inch 2015 retina MacBook Pro and this base model 2015 MacBook. Battery life was better on the Pro but the 2016 MacBook has better battery life so you will be good there.
I highly recommend the retina MacBook. At first it felt too small but after changing the resolution to 1440x900, I can actually see more than with a 13.3 MacBook Pro at native retina.
I will say this. If you haven't typed on the keyboard yet, try one before committing. I am finally used to it but it is a completely different experience than previous MacBook keyboards. If you are a keyboard pounder, it's a big adjustment.
Sorry for the long post, just figured some of the information may be useful.