Eternal and custom build together?

So I was thinking it wouldn’t benefit a high floor build at all to use just eternal items in a build or any for that matter. Well I was wrong apparently there are some items I’m looking into adding to a pve build that are only eternal plus the obsidian afix of course, but I found a few ways to benefit a better build with them. For instance the double PTL and glasscannon externals, or the double add to set , and not to mention the eternal pets element dmg. But I’m now going to replace an entire build and use both a customized build with 2 eternal pieces in it and hopefully have a greater floor and dmg output from it. If you have personal experience with doing this and have benefited from it in floors 1500-2000+ let me know also.