@jPV

Thank you very much!!
Shift+LMB did not work. I guess because the wrong/correct screen resolution is loaded *before*.

But: With some luck, CTRL key work.

And I guess I have found the reason why I am having trouble: It is due to my monitor.
Booting with CTRL key I got some standard screen, as you described. If I then set the sreent resolution to 1920x1080 - my Philips Brilliance 241B has 16:9 format - I immediately get the info: Wrong screen resolution. Set it to 1920x1080@60Hz. And the screen get black.

Okay, I again did the procedure and had a closer look:

For the X1650Pro I only can choose a 1920x1080@76Hz. Obviously my monitor cannot display that.
Now I have changed to 1280x720@60Hz: And this does work - but of course is not that fun.

Funny enough: If I am remembering correctly, for my HD5450 there also is only 1920x1080@76Hz available but the monitor can display it. Has anybody an explanation for that???
Could this has anything to do with HDMI connection (HD5450) and DVI connection (all X-cards)??

And is there any poosibility to add a screen resolution of 1920x1080@60Hz for the X-cards?

Thank you!!!