Will you have the power to pull the hills in 5th gear?
Boy, is THAT a loaded question!
Let me tell you about MY expertise in this area.
Elevation above sea level MATTERS.
I live 9,000 feet above sea level (2,727 Meters, for you metric folks).
My STOCK 4-door with the 1.6L 16 Valve engine can't make it up to the Eisenhower tunnel on I-70 (elevation about 11,000 feet - 3,353 Meters) in 5th gear. It's down to 4th or even 3rd on STOCK TIRES.
My 2-door 1.6L 16 Valve - the Gnewt - with 31 X 10.50's (soon to be 33's) even with the 5.83:1 Ring and Pinion gears, is DEFINITELY down to 3rd gear, and maybe even 2nd on a bad day.
Don't worry so much about climbing those hills. You'll survive a downshift!