Made the trip in 2006.
My wife and I sailed our Caliber 40 LRC from Rockport, Texas to Isla Mujeres in May of 2006. We were headed to the NW Caribbean and are still here in the Rio Dulce, Guatemala getting the boat ready for another cruising season and will be returning to Texas this June. We are considering returning via the Eastern coast of Mexico but as you know, not much is written about that. There is a cruising guide by Rains that covers the Mexican Gulf coast and includes information on Progresso.
We chose to go straight across in late May. Our reasoning was that we could avoid the cold fronts, the summer thunder storms were not geared up yet and the pilot charts indicated relatively calm winds and seas at that time of the year. Our crossing was relatively uneventful from a weather perspective. We do know of boats that have gone into Progresso instead of Isla Mujeres and had no problems. The pilot charts will show you that the prevailing wind is from the SE so be prepared to motor sail. Seas at that time are generally calmer that in early spring. Based on anecdotes from others, we would definitely not go across in the winter.
We had engine problems and were delayed but we made the crossing in 8 days and would have been finished in 6-7 without the problems. Oil wells are not much of a problem past approximately 100 miles out from South Texas. Some cruisers do take the option of going to Florida and crossing from Key West. We did not have the time to do that and have not regretted our decision. I'm sure you have heard this several times but it is worth repeating...for a Gulf crossing pick you weather window carefully. Hope this information is helpful.