Difference in 4mm to 5mm derailleur housing for routing purposes

Hello. I was just wondering if there is any noticeable difference in the 4mm derailleur housing to the 5mm derailleur housing in terms of ease of routing. My bar setup demands a very tight fit and the 5mm derailleur housing is a bit too bulky and difficult to shape/flex (this is only an issue at its entrance into the shifter/brake levers). The brake housing is fine, it just that damned derailleur housing. I understand the drawbacks of 4mm housing (including plastic ferrules and arguably worse shifting capabilities, which I'm not too concerned with). I just wanted to know whether 4mm housing had enough flex over the 5mm to warrant a switch. Thanks.

The routing is going to be fine. Depending on what type of cable stop you have, you might need a ferrule for that, but they are so cheap, its almost free, and you can get them at the bike shop.