Melchior is a GP for me. I definitely think it's way too over the top for real life use; I think it would have a lot of issues with proper pronunciation and spelling. But I secretly like it. You might not be aware of what I think is the main modern-day association with Melchior- it's the name of the main character in my favorite musical, Spring Awakening. They call him Melchy for short in the show. You could also go with Mel.
Marcel is elegant. I wouldn't consider it myself, but I wouldn't mind seeing it around more.