In another thread I read that the little-endian notation speeds things(?) up. Has someone info on what exactly it improves for Bitcoin?
Almost all CPUs these days work natively in little-endian. To operate on big-endian numbers, additional byteswap instructions are needed.
For most things, I think this effect is negligible. Network protocols need a convention to represent things, and Bitcoin's creator picked one. The actual choice barely matters.