So I was getting some lag whenever I enabled the stress view. Turns out, every beam is drawn as a high poly cylinder. While extremely pretty, it runs like crap. Images don't quite show it, just look at them in game to see the insane level of detail.
It's not because the cylinder, but because there are about 400 beamng changing colour simultaneously (same happens if you use the node debug on an object with lot of nodes). It's a T3D limitation at the moment, maybe in the future there will be a way to speed it up
Beam stress debug adds about 700000 polygons with T75, so I think the cylinders are at least part of the problem. Beam highlighting uses similar cylinders and it's also slow if you highlight every beam. Seems like that feature is broken now, though.
Cylinder drawing is semi (non intended pun to the above post) slow. I used it ages ago and reverted because it was too slow for me.
Currrent debug render is WIP and very unoptimized... sorry for that. Try debug in simple levels for try avoid lag.