There's a 2015 Ecoboost convertible near me with under 26,000 miles. I've driven it and decided I could be happy with the turbo. I am here, looking for tribal knowledge about the first model year of the S550's, and the Ecoboost and convertibles in particular. Anything stick up I should be on the lookout for?

I will miss my GT. But with 197,000 miles on the clock, I know it's time to think about making a change.

 

Seems to me that "I could be happy with" doesn't sound like you're completely sold on the idea. Before making the purchase you need to be sure that this is what you really want. Your commute might make the extra miles per gallon worthwhile. On the other hand the GT retains more value over the years of ownership. I don't think there is anything wrong with the ecoboost. You have owned a wide variety of Mustangs and should go with what you think would make you the most happy.
Good luck on your future purchase.