In the original ARM design the multiple register transfers were much more efficient than the equivalent single register transfers because of the simple architecture which had an inherent load delay (it couldn't fetch an instruction and a data word in a single cycle). When they switched to the Harvard model they lost their advantage.

Talking of the ARM reminds me of older heroic feats of assembly-programmed internet software in the Acorn days, such as Ben Dooks' all-asm TCP/IP stack and Jon Ribbens' web browser. Probably not been done that often...