I used some of my main Fed toon's EC to buy a Cmdr level Excelsior and equipped it with Mk XI gear. I tested it against my buddy flying a Galaxy Class Retrofit in a one on one challenge and he mopped the floor with me. I was laughing as he blew me up! Ship works well in PvE, but PvP is suicide.
I like scale with your level shuttles and the Connie's scale with your level phasers, but a starship might be too much.
I think the D'kyr looks cool, just debating between that or the Nebula refit. I would reall prefer a galaxy refit, excelsior, or sovereign class, but since I use science ships, doesn't work that well -_-;