Lyne have you updated at all? I would STRONGLY recommend you update using patch 288741 - it does help quite a bit - but still its not as speedy as V5I - I think there is still a mem. leak somewhere, but it does improve speed when moving things around and the amount you can import etc etc.  Keep in mind more of the complex features are still not working or not up to speed yet.

Also, turn off openGL lighing this helps enormously & for me I found this feature not very useful to begin with - just another mem hog.