Ok. Actually that would change the defaults for all sliders. You can change the values for each of the sliders by inserting the attributes slideshow_speed and animation_speed into the shortcode.
If you need to control speed for only the slider post, try to put insert shortcode attributes slideshow_speed and animation_speed to the slider post. You can accomplish this by editing the file single.php in theme folder at line number 48 from
$output = '[responsive_slider type="featured"]';
$output = '[responsive_slider slideshow_speed=6000 animation_speed=800 type="featured"]';
and making a similar change in line number 240 in file framework/functions/blog-content.php file. Pls experiment a little with these values to obtain your desired slider speed. Thanks