Dont worry, you will be able to use both KDE 4.3 and 3.5.
As for when KDE 4.3 is expected, so far its expected to be released on the 30th of July.
As for KDE 4.2.2, eh its so close to the KDE 4.3 release right now I would not really bother with it.
I found KDE 4.2.(3,4) more stable than other 4 releases.
For KDE 4.3, i think its quite different from kde4.2.x.
I tried M2, and it looks like very promising than previous releases with some major updates and alot of bug fixes.
I m sure, KDE4.3 will rock and it will be a stable release so far like kde3.5 series.
KDE4.3 is releasing on 28th July 2009. Schedules/KDE4/4.3 Release Schedule - KDE TechBase
Yes, I have not updated anything (including Kernel/System Updates) since appx last 2-3 months.
user@linux:~> uname -a
Linux linux-xxxx 18.104.22.168-3.2-pae #1 SMP 2009-02-25 15:40:44 +0100 i686 i686 i386 GNU/Linux
Because (as I mentioned above) I do not want to mess up the functional KDE 3.5.10 install while updating to latest KDE 4.2.x / KDE 4.3b. The last update I did was before the KDE 3.5 & KDE 4.2/4.3 packages were renamed.
I am actually running the Factory and FYI the Extra Apps is no longer.
And I also have kde3 with no problems. You need a bit of SUSE magic to manage kpowersave with kde4, you actually have to add it kde4 autostart and set disabled, otherwise it conflicts with powerdevil.