From what I have read the 75E dish will not be big enough to get a stable signal in Central Mexico. You will need two separate dishes.
You will not
need two dishes for a stable signal, nor will you need the larger dish. Those of us using Star Choice in Mexico, south of Guadalajara and west on the coast, have either the smaller or the bigger elliptical dish, and both work fine. The bigger the dish, the better, that is all.
A DUAL LNB is the key ingredient, whether the dish is elliptical or round, to pulling in both satellite signals. As mentioned before, though, to get Hi Def, an elliptical dish is a must.
Please note that those of us in Mexico who are receiving Star Choice are expressing facts... not opinions.
Also, in terms of stable picture and the rainy season: the newer and bigger the Star Choice receiver, the better the signal reproduction. The 505 and 535 are able to lock into the signal more quickly and reproduce it with more stability. They are affected by rain, but will adapt much more quickly than the lesser boxes... 10 minutes or less, as compared to perhaps 30 minutes or more in some cases.