I've updated the project in the first message, but you can access it from there:
Now are displayed FPS, renderer, number of objects and number of physical objects. The last count is "home made" so I could have missed some of them but I don't think so.
I've "cleaned" the project and on my work computer, it's perfectly fluid but it has always been. At home, it's a little bit slower but it remains totally acceptable.
I'll retry on the computers on which the results were somestimes terrific and let you know about the hardware etc...!
Thanks for you answer anyway!