7yuv uses 64-bit file offsets for all operations to support large files. It does not have 32-bit (2 or 4 GB) filesize limitation like most other programs.
Due to smart memory handling there is also no system memory limitation: Only the visible and edited parts of the file are kept in memory. Therefore you can open and edit files of any size regardless of available RAM. (Of course a baseline of a couple of MB of free memory is required.)
Filesize does not affect the speed of scrolling or editing data.