1.) In general, the gain and beamwidth of an antenna dictates the shape of the coverage. That being said, each antenna has its own propagation characteristics. The best thing to do is buy another 2.2dBi omnidirectional and lab it up.

2.) Was your original site survey conducted using the 2.2dBi dipoles, or was it strictly predictive? If the survey was done with real world data from your old antennae, then coverage may be quite different with new hardware. My suggestion would be to do a new survey.

3.) A URL? You mean which company should you use?