My new S3 came with W10, so I'm not certain W8 would be faster or not. The only lag I've noted using my S3 is what I expected to see running an Atom as opposed to an i5. The delay in general is only in that context - comparison between an Atom & i5 chip. I find the S3 to be fast enough for me to do any sort of office work that my job calls for, even though I use my desktop for daily work activity normally. I have the same software on my S3 as my desktop and the S3 runs everything the desktop does (sans gaming). When I speak of gaming, I'm talking bout iCore style gaming rather than Windows Store stuff.
I'm sold on the S3. Good product, light, compact, cool/quiet, good screen, good type cover - does all things well for me!