Thank God for the black keys indeed! 
Actually if i were you, i probably would continue working on Eb and Ab. A lot of gospel songs use those two keys more commonly than Gb.
Funny enough i am really good in C. The great thing about the "black" keys is that the chords use very similar voicings. Honestly if you can play in Db then Gb is a piece of cake to play in. The "white" keys just have wakward fingerings IMO.
Yes, Fenbox is right, let's keep the Gb club exclusive
On the 2nd part Fenbox, it really depends on how you practice in each key:
For me, I try to play the same voicings with all the keys..maybe it's a thing or 2 I do in Gb very well that I can't do in the rest of the others.
Bb (a black key) makes me feel like I'm in a tiny enclosed room (but hey, it felt good playing some songs with it at service today
)..
B is a "white" key on the other hand, & once you get used to playing that E instead of F, you feel quite free to flow.
D-A-E have a similar feel.
F & Bb.
Eb & Ab.
Gb-Db & B feel alike
C& G are also great to play with...my fingers just move so freely when I'm in those keys..I don't know which 1 I like better
