50% more battery life than the 4, fanless options for the m3 and i5 versions, on screen support for the surface dial, and a new hinge that lays a little flatter seem like the big changes. It's largely an incremental improvement.
More battery is a big one - I love my sp4, but I think (even with the improvements with the pro) they should have added a few 100 grams for more battery.
Fanless i5 would be nice - my sp4 i5 isn't loud, but quiet would be better.
Was hoping the new sp would be waterproof though (it's the only remaining "obvious" improvement I see. We'll that and enough gpu power to drive vr - but I suppose we're still a few years from that in a small, light, quiet battery-powered device).
What's new compared to SP4?