Thanks, Frank,Richard and Bill for your comments.
It more or less confirms what I thought.
In my situation I will need a fast cpu and large ram.
As I have to replace my old PC anyway, I will built a new PC later this year, so let's see how that new PC can handle both plugins and real time sample playing.

Will keep you informed.

Thanks again, Fred
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Keyboards/Sound Units: Kurzweil 2600S, Roland VR-760, Acces Virus C, Roland G-800, Akai AX60, Minimoog, Machine Drum, Roland R8-M, mediastation x-76