I love writing 6502, or maybe just 8bit assembler in general . I got hooked after writing some NES games. Writing efficient (NOT “performant”) code that should not be possible is very addictive. Stay away if you value your time
I later used Z80's[3] at Uni for hardware projects, again programmed in assembler (via EEPROM which was less convenient, but we were practising for "embedded systems" development) which was fun too.
The only thing close to the BBC Basic experience was Delphi which supported inline assembly, which I used once to do some bitmap manipulation faster than I could convince the compiler to manage.
[1] a budget version of a BBC Micro Model B for most intents & purposes [2] and later a BBC Master Series [3] they basically started life as knock-off 8080s, the 8-bit chip that lead to the 8086/8088, so it'll feel familiar if you've done any old x86 assembly
Tools are everything here. Get a good emulator/debugger and assembler.
Lets say you had a 6x8 character cell or a really small sprite for graphics, unrolling the loop would make a copy about 2x faster but would cost about 40 bytes or so.