I've got an SP4 8gb, 256gb, i5, primarily for editing on the fly. I use Lightroom and PS Elements with multiple D800e and M43 RAW files and it's easily man enough for that.
As long as you've got the SP4 keyboard (the mousepad is a lot better than the SP3 version), maybe a good bluetooth mouse and a reasonable knowledge of the keyboard shortcuts you'll be fine. The screen is fantastic quality although there are some scaling issues with some Adobe products. I forget which product releases I have and they may have solved the issue with subsequent versions of the software. I've got used to it now so have never bothered eliminating it.
If you're going to get one for editing get a mid level spec (like mine!). The lower spec version has a processor which runs silently & cool but probably doesn't have the grunt necessary for frustration free editing. Storage limits have never been a problem for me. I do have an additional 128gb permanently fitted via a micro SD card as a back up should I need it but never have.
The keyboard is an additional cost but well worth it. I bought my SP4 from PC World when they were running the 10% cashback offer so I'd keep an eye out for similar deals. I got the keyboard via Amazon at virtually half the price PC World were asking. although it seems PCW will have one offer or another on a particular colour. Don't bother with the fingerprint recognition version, the face detection on Windows sign in is very effective.
I don't find it particularly laggy, even when compared to the big laptop I edit with at home (i7, 16gb, 1.5gb SSD, Geforce GTX770).
Any other questions let me know.
Cheers
Mark