I'm looking at doing a HEMA comp in Poland next year, which means I'll probably need to pick up an ultra-light, Polish-HEMA-federation-compliant arming sword. This got me wondering, how many surviving examples do we have of real medieval arming swords that light?

Has anyone done any research on what went in to producing arming swords that much lighter than the norm, and how their capabilities compared to their heavier cousins?

The classic IX.950 in the Royal Armouries springs to mind immediately. I've played with this piece a bit and it's really a joy in the hand. Yes, the listed weight is accurate.