Re: Measuring wind speed
I don't think the directional and crosswind features of the 4500 are really needed, unless you just have a surplus of funds and like gadgets.
Ballistic programs just want the magnitude and direction of the wind. You can judge for yourself the wind direction to within 30 degrees or so, and that's perfectly adequate given the other uncertainties associated with the wind speed, some of which have been mentioned above.
A 4000 is handy if you're going to use Density Altitude firing tables, because it computes DA for you.
If you're not going to do that, a device which measures the wind speed, temperature, and pressure is fine. Add humidity if you're going to extra-long distances - at distances at or under 1000 yards it may be ignored.