From my own experience I use this rule of thumb: If you have a hard edge you also need to separate the UV's along that edge to avoid artifacts due to the texture filtering.
I agree with Illusive, give those edges a bevel, it will make them stand out a lot more. You also might want to loosen your control edges, they are really tight atm.
You can create support edges to get that, in my image the first model has support edges with no meshsmooth and the 2nd one has meshsmooth with a subdivision so you can see the result.
Quite often edges get broken and separated when exporting out of Unreal, usually along UV seams and hard edges. If you weld everything it should allow you to use quadrangulate.
As long as there's enough triangulation around the torn edges and you create your 'torn metal' tileable texture(s) correctly to paint on those edges, it will look great. It should also be very performant.
It means that those edges are not connected and you actually have a gap. I am not sure how to fix it in max, but in Maya you can just collapse those two edges and its fixed.
Looking cool, One suggestion I have though is that you need some harder edges. I'd go in with the h-polish and dam-standard brushes to get those edges. Keep it up.
Hey Paul, is there a reason why you pixelate some of the outside edges of your textures (outside edges of your UV shells). Are they acting as base colour swabs? Really great work man!
at some time I need to head over to the wiki and look into 3ds max smoothing groups. Always confused by them since in Maya we just have soften edge and harden edge.
Really nice work Adam, and thanks for the insight about the thin edges vs thicker/softer edges. Would you mind giving some insight about your render set up?