What??
The numbers you guys are talking about is freaky! I use a double ply poly, inzer hphd blast and it gives me between 30-50 lbs depending on how strong I am that day. I have no doubt that a denim would give you more they have less give than the polys. Also There aren't many federations that allow more than a single layer poly. I lift in the USAPL and APA/WPA. USAPL is a single ply poly ONLY, NO denim, NO velcro or open backs and no double layers. The APA is different, they allow up to a double layer and fast/open backs.
As far as weight increases, a single ply poly will give you 25-30 lbs and a double will give you 30-50 lbs. My best raw lift is 330,(touch and go), my best shirted lift is 375,( comp. form).