Thanks for the information ( bedankt voor de informatie! )
My system looks as follows:
Lightroom version: 4.2 
Operating system: Windows 7 Ultimate Edition
Version: 6.1 
Application architecture: x64
System architecture: x64
Physical processor count: 8
Processor speed: 2,9 GHz ( i7 )
Built-in memory: 12286,4 MB
Real memory available to Lightroom: 12286,4 MB
Real memory used by Lightroom: 398,2 MB (3,2%)
Virtual memory used by Lightroom: 384,6 MB
Memory cache size: 220,7 MB
System DPI setting: 120 DPI
Desktop composition enabled: Yes
Displays: 1) 1920x1200
Application folder: C:\Program Files\Adobe\Adobe Photoshop Lightroom 4.2
Library Path: F:\Lightroom 4 catalog\Lightroom_4_2012_03\Lightroom_4_2012_03.lrcat
System drive is a 10Krpm
Library drive is 7.5K rpm
At the moment I have 102.300 pictures in the catalogue. Of which 3/4 is off line.
Catalogue is 196 Gb included one back-up and AFTER optimisation.
113.564 files and 55.756 folders
I have tremendous problems with performance. e.g. after 15 to 20 images work in develop it gets fast as thick syrup!
So I close LR and restart the system and work for another 15 to 20 images and then the same protocol!
Not very good when you are under time pressure!
The same catalogue with 98.000 images in LR 3 I had much better response and had never to close LR and start again. What I saw was that the performance with Lens corrections went down.. So I left that out and only did that at the very end.
After deleting the History of all current projects >250 images, I see a bit improvement but after working on 30 images
slowmotion coming in when opening a new image. So, yes deleting history helps but is not a defenite solution!
Anybody any other than spending again a 3K euro’s on a new system?