I just opened 1.5GB binary file and it ate 2.5GB RAM according to Activity Monitor.

I tried to open 20GB single line text file and it started to eat RAM. I killed it at 60GB as I only have 64GB RAM.

So at least modern version does not seem to work well with big files.

vim does not seem to work either.

Ken is correct. IIRC, the very first version of BBEdit back in 1991(?) could handle files significantly larger than memory (on a system without memory mapping, no less).