JS Resize function for div containing a a slideview slideshow and set as a page background
Found two options: cycle2 for which the project is still in development stage:
http://drupal.org/sandbox/BenYoung/1832338
(and did not work when following the installation guidelines, since I never got the Cycle2 option in the dropdown and needs jquery 1.7 which apparently causes a lot of trouble)

And one that is actually fully functional
Flexi Slider here http://drupal.org/project/flexslider , for which I found also this great tutorial here http://coldfrontlabs.ca/blog/creating-responsive-image-slider-galleries-adaptive-images-drupal-7.
Strange that they're so well hidden when adaptive design and full width sliders are so requested now...

Now it works as I wished for it to be, except for one thing I will ask a different question for.