Hi. I'm with my 3rd A320 operator (all LCC-s) at the moment and so far the magic mark was always 300kgs. Anything above it should be well reasoned by a quick call to OPS. Having said that i have never seen it written in any of the manuals or other controlled documents. It was continuously mentioned however in newsletters, fuel savings emails, crew infos, etc. Smart way of bypassing the regulator but still trickeling the restriction down to the individual PIC. Cheers