controlled enviroment or not obviously ie a garage with a/c and heat. If it sits outside I would say maybe 8 years on the belt personally but in a garage I would push it to 10 maybe more. 5k miles and 5 years is nothing really to worry about in my opinion. The most wear comes from miles and heat/cold conditions while in motion. Just my opinion, never snapped a tbelt and mines sitting at almost 7 years/ 30k on it for my z32.
My 2 ladies and dads 350z wishing it was as sexy as my girls :)