You're getting varying opinions here, but if you buy the 6 x 6's can I have your stock pipes? When I was looking to buy a Valk, I rode a 2001 Interstate w/ 6x6 without baffles in them. The bike came with full-face helmet-to-helmet communicators wired through the bike. The 6x6s were SO loud, that my friend and I could not talk above about 2000 rpm. Going down the highway, I had to pull the clutch in and coast just her to hear me and me her. Speaking of loss of power, there's really a loss of power when you have to pull the clutch in to talk or listen to your passenger!
A month later, when I bought my standard Valk it came with 6x6's on it (drats), but at least with the baffles in. I wanted stock pipes for cruising, but I've got 6x6s by default. I can't find the name of a manufacturer on them, but they look great.
Mixed feelings...they look great...the engine does sound like a Porshe and does turn heads. It's great for going to the local restaurant or pub, but over 20 miles and 2500 rpm, I have learned to wear ear plugs. The loud drone when cruising on the interstate is very tiring. They'd be great if they had a volume control on them. (Hey, just put some good speakers on your bike and buy a CD of pipe sounds to play while you're going down the road.

)
I've not ridden any Valk with stock pipes so I can't say anything about a difference in power. Money is rather tight right now, but if I could put stock pipes on the bike, I would.