If you've not used kde since 4.4 you're missing quite a bit. For me, 4.4 was still not release quality, but 4.5 finally made it, minus kdepim of course (so kmail, kopete, etc, all the stuff their akonadifying), which peaked at 4.3, before they akonadified kaddressbook and started breaking stuff (I eventually switched to claws-mail for both mail and feeds, and have long used pan for newsgroups and mailing lists, thru gmane's list2news gateway, I don't do IM so didn't have to worry about it).
IIRC they were just beginning to introduce kwin as a tiling WM back on 4.4, and it has gotten MUCH better since, tiling and in general, with a MUCH improved window-rules GUI in 4.7. But there were some (non-kwin) regressions in 4.6, plus of course the whole akonadi breaking kdepim thing, both of which aren't fully straightened out yet, so late 4.5 with the 4.4.10 or so kdepim was the best kde4 so far, IMO.
I don't use either kwin's full window tiling (tho I use the quarter- and half-max drag-to-side functionality that works well for semi-tiling) or window tab-grouping, as I've developed my own solution over the years, an almost maximized title-bar-less window with a pair of half-maxed side-by-sides arranged so I can click either of them or the almost-maxed window to raise (as long as I don't raise both side-by-sides thereby hiding the almost-maxed-titlebar-less) and focus, or simply hover over one that's below to focus it for typing into, without raising it, just making it visible as 100% opaque thru the semi-transparency of the defocused but above window.
It works well for me. In fact, I hadn't realized just how much i depended on the then kde 3.5 window transparency until I tried to switch to kde 4.2, and thru a dual-rooted combination of a bug later fixed in 4.3 or 4.4 and a *HORRIBLY* deoptimized for my hardware default animation setup, 4.2 window transparency (and effects in general) would lag the desktop by HALF A MINUTE or more at times, thus being entirely unworkable, so I had to turn it off.
Ultimately I traced both roots down and both adjusted the config and found a workaround for the bug (by trying and configuring a single kde4 app at a time on an otherwise still kde3 desktop, thus isolating the dual roots), after which I could reactivate window transparency again, and soon thereafter I upgraded graphics so could configure more effects, and the bug was fixed, so I didn't have to worry about the workaround (no actively updating plasmoids on the desktop) any more, but the point is, I found out how much I actually DEPEND ON window transparency from that experience.
As far as I can see from the writeup (tho I've not finished reading all the comments yet), awesome might do tiling, but it apparently doesn't do compositing, so it would appear that window transparency is right out, which means awesome's right out, for me, because I actually USE window transparency, referring to a semi-transparent say documentation or config window on top, while also looking thru it to type my answer to a question about it, while referring to it, into the active window below it.
But OTOH, kwin might do tiling, but I don't believe it has anything quite as flexible as tagging, which now that I know about I'm going to miss as well. But I wouldn't be surprised if it gets it.
So they both have features I could and/or do definitely use, while missing other features I could and/or do definitely use that the other has. =:^(
Meanwhile, to answer your question, originally neither kwin4 nor plasma could handle zaphod mode, separate desktops on each. They're actively working on it and last I read the bugs (4.5 timeframe, so a year-ish ago) it was sort of working in IIRC kwin, but not plasma yet (or was it the other way around?). But 4.6 the then still in development had some fixes that had it /almost/ working (probably about like the 4.2 the kde folks insisted was ready for use, despite its still being late alpha stage broken AT BEST!), basically working, but with some stuff that you'd definitely learn you couldn't do and would avoid after that.
While I use a dual monitor setup, it's as a stacked-orientation RandR mode single desktop, and I've not followed the bugs. However, given the rate at which they were progressing and that it was said to sort of work for 4.6, I'd guess it pretty much worked, but possibly not smoothly, for 4.7, and that with 4.8, it should be pretty good.
FWIW, I'm running 4.7.80 now, aka 4.8-beta1, beta2 released yesterday but I've not upgraded yet.