I recently was able to purchase a SP3 i5 model brand new with Windows 10 preloaded for $600. It comes Tuesday and I've debated keeping it or returning it. Battery life is very important to me and these days I consume data more than have to work on my tablet/laptop.
Therefore, I spent time playing with the SP4 at best buy as I'm considering the m3 instead. Here are some of my observations: I like the thicker bezel on the SP3 and how it feels in the hand even though it is notably thicker & on paper heavier. I don't believe I have fat thumbs, but with the thinner bezel the SP4 kept registering my thumb and zoomed when I was trying to scroll. Holding the SP4 along the bezel to prevent this was uncomfortable. After close to a hour the i5 stayed cool and the fan never came on while using edge. The new display was sharp and next to one SP3, it made that SP3 whites appear warm and whites yellowish in appearance. That said, next to another SP3 on display, the difference was not as apparent from my unprofessional eyes.