I had the copper rings mod on my HD650, was a good mod but I then also tried removing the foam which then negatively impacted the midrange and up I found, not a massive amount but enough for me to notice, so I'd say leave the foam.
Under 300g is light as a feather, Arya/HE1000se/LCD-2 are all well over 400g but thankfully all are comfortable enough to feel lightweight on the head, and something I did not notice before with the LCD-5 is that the leather pad material softens after time with body temp, I guess that took a few days to acclimate properly as now they are rather comfortable, and I never liked leather pads in the past on other headphones or aftermarket ones (Dekoni). Seems whatever leather source Audeze use is rather high quality.
The foam inside isn't memory though, so that will compress over a period of time needing a pad swap, so I'm tempted to see what aftermarket pad options are out there and see if some additional tuning is possible with different pads in the interest of scientific research noting that the stock pads are stuck on with double sided tape (!).
Also slightly amusing, but the more I use the LCD-5 the more I end up liking them, obviously with the new HP-EQ. Don't like the cable still though, too long, too "bouncy", going to see if there are 3.5mm to mini XLR converters I can use so I can just use the Tripowin cable which feels much nicer and stays where I put it.