I have just upgraded to the k550 from my 3 year old setup (senns HD 448, Portapro, HD515, E7) and must say they are just amazing!
The difference in terms of clarity, soundstage and detail is immediately noticeable. Vocals, instruments, bass. Just so much more detailed. Though I don't have enough experience with the GMP 8.35 and the Shures, I can guarantee you that you won't regret purchasing the k550's.