Okay, seriously. The iMac comes with a 395x mobile gpu. It's pretty comparable to the 980m. The 1070m and 1080m don't exist yet. If you guys actually knew more about hardware than nothing, maybe you'd realize that it's not possible to get a 1080m.
iMacs and Macbook Pros (top of the line 15-inch with dGPU) have always used mobile GPUs. Also, illustrators/designers don't need dGPUs. That's why the designers/illustrators at hte tech companies that you work at can use macbook 13 inch laptops and 15-inch laptops without the dGPUs
It's not even 980, its 980m which is significantly slower than 980, nevermind 1080. And the 980m only comes in the $4199 option, that's ridiculous...