Earlier this year I picked up a 5wt switch for the Bow and love it. I feel a 6wt is a little much for the Bow but if you plan to do most of your fishing elsewhere for bigger fish then go for something larger.
Also I thought i'd mentioned that you don't exactly need a spey rod to catch big browns. The bigger fish are generally not found in the middle of the river, most guys use a SH 6/7wt rod fishing tight to the bank. On the other hand if you just want a spey rod that's cool too, they are a ton of fun to cast and there's really no reason why it wont work for what you are doing.