Set your models to one smoothing group and try to have the least amount of modifiers possible. Also, avoid RT lights of the Nitrous, and make sure your UV's are NOT stressed or set outside the 0-1 space. These right the top of my head kill Max's Viewport.
Stressed UV's the ones which look like they've been shot into a singularity black-hole across the room. Basically, ones that overlap in very small part of the UV editor, and which don't untangle, even with high relax values and require you to redo the UV's since they're a lost cause.