Bigger gears in the back makes for an 'easier' ride, where as bigger gears in the front makes for a 'harder' ride.

What type of rear derailleur do you have (shimano 600, I'm guessing)? Most can accept pretty big cogs in the back, but some have limitations. It would probably be easiest and cheapest to get a cassette (or is this a freewheel machine?) with bigger cogs. You can also just replace chainrings (instead of the whole crankset), again with the limitation that some FDs only accept a certain range of sizes.

peace,
sam