Switching to Lower Gears for Climbing
A cadence of 70 RPM while climbing is not unusually low, so switching to a lower gear may just encourage you to slow down instead of making you more efficient. But the only way to know for sure is to try it and measure the difference.

There isn't necessarily a right cadence. The article Technique - Pedal like a pro reports that seven pro cyclists (a small sample, I know) dropped their cadence from 80-100 RPM on the flats to 60-80 RPM on a 5% grade. Although Lance Armstrong is famous for climbing at 100+ RPM, this does not seem to be common.

I personally do better when I climb at around 70 RPM than I do at a higher cadence. The higher cadence just causes me to get out of breath faster. But this is different from person to person.

In the end, there's no harm in trying a different gear and seeing what works best for you.