FWIW, kde4's quite good once it's built with the semantic-desktop cycle and space-stealing malware turned off. On gentoo, that's a flip of a few USE flags and a rebuild.
Of course that means no akonadi, since it's semantic-desktop integrated, which means no kdepim (including kmail) of any sort, since even for stuff that doesn't (yet) require akonadi directly, the kdepim libs stuff pulls it in as a mandatory dependency, but being rid of that message disappearing-trick software was actually what triggered the whole OK, with that gone, I might as well turn off the whole semantic-desktop thing in the first place.
Now kde4's nice and lean and snappy, better than kde3 was. =:^)
Meanwhile, I too ran konqueror for years. Unfortunately, in kde4 it became quite apparent that the kde and konqueror devs themselves considered it little more than a toy. Because they insisted kde4, including konqueror, was ready for normal use, /years/ before it had a proper SSL/TLS certificate management GUI... this in an age when not only individual certs need deactivated, but whole certificate authorities! Similarly, there was the infamous double-form-submit bug of kde 4.6.x, introduced in the middle of a stable cycle, but worse than that, taking two monthly bugfix releases to fix.
So there's only two conclusions possible about the kde/konqueror devs. They either don't care about security at all, in which case the browser with its primary remote attack surface exposure is "just a toy", certainly NOT fit for "normal use" like online purchases and banking (double-form-submit, security cert management issues, both VERY bad problems to have there!). Or they care, but they specifically consider konqueror no more that a toy that nobody would use for "normal use" like online banking anyway, so much like say the comic-strip-plasmoid, it's just a toy, for non-serious entertainment purposes only.
But firefox with the noscript and request-policy extensions (plus perspectives and dnssec validator) is both higher security and higher compatibility, with the noscript and request-policy extensions in particular both much easier to work with than having to dig thru page code to figure out what to try enabling in konqueror to hopefully have a page working without google-analytics or the like. There's no way konqueror could keep up with noscript alone, without a much larger userbase to support it. So it was time to switch in any case.
I do wish kde's and firefox's bookmarks could be integrated, tho. That's the remaining frustration. I keep a classic-menu set to bookmarks on a panel, and with the appropriate kde setting they launch in firefox fine. But it's one-way-only. I have to launch kde's bookmark editor to save new bookmarks, and that's a huge pain compared to the integrated bookmark saving, updating both the bookmark plasmoid and the konqueor bookmarks themselves, that konqueror had. Oh, well...