I'm still not clear of the advantages of calcultating gears with gain ratio vs. gear inches. I use gear inches, and I think 70 gear inches is a good starting point. Many people ride close to that ( a 42 x 16 is 69 and a 42 x 15 is ~73.5 ). Hills will be fine, but you won't be spinning like mad on flats. You just won't win any sprint races. People on flatter grounds will increase up to more like 75, and maybe people with more hills might drop down to 68 or so. FYI, your current gearing puts you at about 61, which yes, would make me laugh too.

Go for 70. Most people seem pretty happy around there.

Here is the link to the calculator:

sheldon brown gear calculator

Be sure to switch it to gear inches and put your cog size in one of the boxes where it says custom cassette. You can enter in numerous chain ring and cog sizes at the same time if you want to compare.