Without load, the voltage should be linear against RPM, in other words double the rpm and the voltage will double. What load (resistance) did you put on to get the 3 amp? Also, with no laod (open circuit), what voltage do you get at 160rpm?
What tip speed ratio will you blades have? If you know that, you can calculate the RPM for a given wind speed, using the radius of the blades and some simple maths.
Sorry about problems with the site - the hosting service I use is free, but a bit flaky. Seems to be working now.