As a continental European working on farms in rainy New Zealand I've learnt a couple things:
Oilskin in rain is workable - best in the form of a vest. I only used my oilskin overtrousers in downpurs.
Waterproof garment breathability is paramount. Heavy physical activity = perspiration. One will get soaked in sweat in a couple of minutes even in a 100% waterproof fabric with no proper ventilation. A serious limit for oilskin overtrousers.
An oilskin vest designed for farm work is worth gold. It has a handy extended lower back side a.k.a. drop tail. It keeps your bum dry even bending over.
Choose the vest size for a relative loose fit (even in a woolen jersey). You're not after the looks but practicality. The special fit caters for a) unrestricted mobility, b) proper ventilation: body movements will pump out damp air under your armpits, c) protecting kidneys and lower back from windchill. Speaking of which the upturnable lined collar is fantastic. It can be fixed snugly around the neck with the front zipper being pulled fully up. It gives a great comfort when rain is combined with cold and wind.
Concerning durability: my Norsewear vest has been serving me for over 22 years.
Wool is magic. It is warm even when soaked. A good woolen jersey is a must have.
