I'm not Ian, but I'll go out on a limb and say you are not going to get a pad X of 580mm on any bike with an integrated front end. And at 5'11" sitting -7 on an ISM, you're just weird. You need a classic P3, 56cm with a 14cm stem and some super fore and aft adjustable bars.

I'd like to see a photo of the position though. I'm 5'11", ride a 155 crank, ISM saddle at -2cm, with a Pad X of 550 and I am really stretched. You're talking about roughly 3 more inches off (saddle to pad) "reach".