imho you will definitely notice 5mm.
170s seem stiffer – not so much in a rotational direction but they seem to resist flexing in-and-out when you weight the pedals – and have a bit more ground clearance.
On the other hand they’re harder to crank compared to 175s
For long days in the saddle I would go for 175s but for a couple of hours ragging around the local loop I would choose 170s.
Oh my word, post of the week for me. Made me chuckle.