DT, no disrected intended, and I'll state up front that you are a very knowledgable bro and an asset to the board. However, the idea of training a body part once a week as being optimal is not supported in any scientific literature, has no positive research to back it, and most physiologist will tell you that frequint training yields faster adaption. Furthermore slyder is an enhanced athelete. His use of gear will dramatically increase his recovery ability.
Not to sound like a broken record, but arnold trained his bi's and tri's three times a week, and had arms on par with alot of pro's today who outweigh him, and he didn't have access to hgh, insulin, igf-1 synthol or many of the other substances available today. Are we suggesting that if he had cut back to once a week they could have been 25"? I doubt it.
What about current Mr. Olympia, "Alien-belly" Coleman? He does back training twice a week, on seperate days, and still does 2 heavy bicep sessions a week. Would his arms be bigger if he cut back to once? Actually, outside of Dorian Yates, I can't think of any Mr. Olympia who trained arms only once a week, and honesty Yate's didn't have the best arms onstage (I'm saying this as a fan, because I think Dorian was one of the greatest bodybuilders of all time).
I have to agree with Debaser on this one, now that you've trained your arms to adapt to a higher frequincy training, and they have grown while doing so, reducing frequincy may lead to stagnation in their development.