Linux

Other than memory speed, there is one more blocker - your cpu (ish). live usbs do not store the raw image uncompressed, they would be much larger in size. instead, the file system used (usually squashfs) is compressed (usually zstd (default level 3), but could be lz4, or xz, etc). whenever a file is loaded, it is first uncompressed, and if you have enough memory, you can try the load to ram (or memory, wording may differ) option, where, important parts of image are fist uncompressed and stored in memory, resulting in better performance. Now most cpus are fast enough to decompress, so limiting factor still is likely your storage (usb x.y standard) read speed (and if it stably runs that speed, or is thermally throttled), but if you are on a faster underlying source, it can make a difference.

Anecdotely, I use squashfs to compress most things i keep, and it is fast enough for most purposes, but i have observed that for benchmarks, especially single threaded, there is a significant difference. for geekbench 6, my singlecore score was close to 0.6 times of the actual score, when read from uncompressed, or from memory. for all core, score was nearly 0.85 times of the uncompressed/memory score. Would you realistically feel the difference, no imo. I even have a file system level compression (btrfs, zstd, level 3), and i do not feel a significant difference.