Regina--The custom bike will last you a long, long time and I remember all the problems you were having w/your arm/shoulder last fall. I used some of the $$ my parents left me to get my custom Lunas and I don't regret it. Riding those bikes is a treat. You'll be able to outfit your Seven with the wheels you want, components, etc. Plus the anticipation of getting it, after planning it, right down to the color, is such a treat. In the long run, I expect you'll save money by going custom (won't want to replace anything on your Seven).
I know lots of folks enjoy carbon frames, but I'm a steel girl. I'd love to get a titanium bike eventually. Carbon doesn't interest me because I love the ride steel gives me. What type of material is the Seven you want made of? I thought about getting a Mudhoney when I was looking for a custom 'cross bike. It was only because I loved my Eclipse that I went w/Luna for the 'cross bike. Seven has such a great rep, too.
You ride more than enough to justify investing in a custom "machine." You deserve it, so follow your heart.