I would go with the 32c tires. Also, make sure you've got fenders and good rain gear. Yes, I have biked in Ireland.
Speaking of tires, and Ireland.
This is my '89 Schwinn Voyageur that I rode to NY State in the summer of '14, planning to ride the UK and Ireland on it this summer.
Fortunately the center-pull brakes could be adjusted to fit 700c rims, and the original derailleurs and friction shifters work with 44-32-22 chainrings and an 8 speed 11-34 cog (can't get on the little 11 tooth cog on account of lack of clearance). I can get down to 17 gear-inches on the granny.
Where I'm limited is tires and fenders, they just didn't anticipate fat tires in '89. The front fork barely allows a Bontrager 28-35mm fender....
And while I could probably fit a wider fender in back, there ain't oodles of room back there either.
(Pardon the grime, I rode it to work today)
I've been running 700c x 32 Conti Gator Hardshells without problems thus far, a relatively narrow tire for that width but even so there isn't a whole lot of clearance inside the fenders with them.
I like Continental tires and I thought to try "real" touring tires like Conti Top Contact or the Conti Touring Plus for this upcoming tour but it does seems like there's a chance they won't fit inside the fenders.
Is there a big downside to touring on Conti Gator/Gatorskins over there?
Thanks,
Mike