Keep in mind that going from 1.55 rod ratio to 1.60 is more dramatic and makes more of a difference then from 1.70 to 1.75. Just like camshaft duration and compression ratio it only helps to a point. Someone mentioned Smokey Yunicks says go for the longest rod. For his type of racing this was probably true. They never saw more then 500miles and probably never saw anything under 5000rpm. For the street this couldnt be more wrong. Johngrass hit it dead on, its not about long or short rods, its about how you match your setup for it. To take advantage of it, you need to match the cam, even more important are the heads. The intake runner size is very important when considering your rod length.
IMO anything above 1.7 is not worth it. The advantages are so small that its not going to make a difference unless your a professional racer limited to a class and every .5hp makes a difference. Your money could be spent somewhere else with probably better gains per dollar.