Unrelated to korganizer, sluggishness in kde caused by incorrect network
configuration.
This is what happened, in a dist-upgrade I saw that package ifupdown was
being held back and not upgraded.
Tried to force upgrade but it wanted to remove half the system, so I
passed.
Then I saw that there is another package in repo called ifupdown2, so I
installed that one, which removed ifupdown.
That is when the sluggishness started.
So I dist-upgraded today, purged ifupdown2, installed ifupdown without
problems, rebooted, and lo (pun intended) and behold, kde was back!