Hi, up to WP 3.3 having more than 50 or 100 pages in WP often slowed down the performance. It was recommended to choose an url beginning with a number.
Then it was fixed in 3.3, this post explains the details: [ottopress.com...]
As it is very "technical" I don't undesrstand this solution completely.
Is the problem fixed now however I create my permalinks, with or without using the permalink tool of WP, whatever permalink setting in WP or manual creating/editing of the url-slug I choose? Or is there a case which is not fixed?
after a quick read i would say the case where it isn't fixed involves large enough numbers of URLs and URL structures of sufficient complexity that you probably won't scale to that point. in other words, you probably shouldn't worry about it.
the problem was with the use of %postname% and that has now been fixed, with significant effort by the otto guy whose explanation is linked above.
I use %postname% and I have a couple thousand URLs per site, and as many as 3000 simultaneous users on each site, and I have measured performance *copiously* and not had any problem over the last year. The problem is fixed.