Adding Class to views row if View style is Unformatted list / Content
You can try do this later in process or template, when the $vars['rows'] is flattened. You can pull all instances of field_breite out of the flattened row and put them into the classes of the row. For this the field_breite has to be in the custom view mode of course. This would be not so nice for coding, but much faster.

I would code it like this in mytheme_process_views_view(&amp;$vars), but I'm sure you need some debugging:

Go row by row in $vars['rows']. Search the complete field with preg_match() by using the html tags of the field and set parenthesis in the regular expression to get the field value in $matches[1]. Add the field value in $matches[1] to $vars['classes_array'][$id] to set the row class. Cut the complete field out of the row with str_replace() by using $matches[0] from the first search and an empty string.