I finally broke down and got the SP4. I had the i7 SP3 but decided based on my use that I would just get the i5/128G device which is half the price. I went for just enough rather than plenty in reserve.
I've just spent the last two hours getting everything going on it.
1. Snappy and zippy, similar to i7
2. RAM just enough for what I do.
3. Like the camera login. I am on the move with mine frequently logging in so much appreciated and very quick.
4. Screen is better, not a huge difference but noticeable.
5. Pen palm rejection is WAY SUPERIOR to SP3 that drove me MENTAL. I'm left handed which doesn't help but even trying to trip up the SP4 doesn't work. TOP MARKS
6. Camera I haven't really checked out but don't use it much anyway and don't care.
7. It definitely runs cooler. Even during setup this runs cool whereas my i7 SP3 would heat up (not that this was a problem for me).
8. Like the magnet for the pen. Overall pen is much better.
9. I already had the Pro 4 type cover so typing is top notch.
I've got all the programs going I use MYOB, Outlook, Word, Excel, Skype, Edge and really the RAM is still adequate and performance is as good or better than the i7.
I think from a practical point of view, the camera login and better pen are the highlights of the SP4. Performance is the same. Screen is slightly better.
The battery life was never an issue on the SP3, for me anyway, so I don't think it will be on the SP4 either but haven't measured it yet.
I'm happy so far that I saved my money and went for the i5. I find I generally put stuff on OneDrive and didn't need the extra storage and 8G of RAM, while nice to have, I'm just not prepared to pay for and so far I notice NO difference in performance.