You can use a pressure gauge on the sprinkler heads to measure your pressure at each head to determine what the predicted throw distance would be (http://www.sprinklerwarehouse.com/Hunter-Rotor-Pressure-Gauge-ADJ-p/mp-gauge.htm). The gauge at that link is kind of costly. That website also sells the adapter body that you could use with another pressure gauge.
Also be sure to shop around the various web stores for the best prices. Sprinkler Warehouse has the best price for the standard MP Rotators and 40 psi sprinkler bodies, but are more costly for the specialty MP Rotators (e.g., the MP Corner). EvergreenSprinklers.com has a better price for the specialty rotators and 30 psi sprinkler bodies. Both sites offer free shipping for orders over $149 and the free shipping only took 3-4 days. So shop around for the best deal and be sure to account for shipping cost.