Anne I agree with Hildegard, it won't matter much if you use 32" or 34" as either will give you enough room for your throw. And imho, it's better to have a bit more room on your cable than too little.
Regarding bamboo vs alum....I often prefer one over the other depending upon the yarn I'm knitting. Sometimes I want that bit of drag bamboo gives while other times the drag is too much so I prefer alum. I'm no expert by any stretch of the imagination, I've just found what works best for me through trial and error.