I would definitely put the 34 on. Made a trip to Girona a couple years ago and didn't think we'd have steep hills so only had a 25 on the back. Ended up climbing some reasonably long 12% hills. For me at least it's much tougher to ride close to threshold when my cadence is at 50. I think you should gear so you can ride the hills with a cadence around 90 RPM.