Just an update on this, the Greenway is fine on 23mm tyres. A lot of the section from Westport to Newport is a dedicated path that runs alongside the main road. The Newport to Achill part goes very remote and goes through some absolutely stunning scenery it's like some Irish wilderness, I have visited the area a lot but had never seen some parts that the Greenway provides access to.
There is a fantastic pub called Nevin's about 8 miles out of Newport, the food is really very good and is locally well known. There is also a tea shop called Yvonne's but it was closed as we went by. it was opened by a retired Garda (policeman) in memory of his daughter who sadly died in a road crash, the cafe comes very highly recommend locally.
As some have said the distance is not at all epic but if you are in the area it is well worth a visit. The amazing thing it has done apart from tourism is to make some of the locals more active with lots of people using it for a daily walk now and of course bringing people in to cycling. I rode it with my kids and met up with an uncle, he was a fine example of a person that would not be cycling were it not for the Greenway but now he cycles the entire route twice a week.
