5 gal. carboy w/ 1" blowoff for primary

I have a 6.5 gal. and two 5 gal. carboys and so far I've been using the 6.5 for primary. The krausen builds up a couple inches and then settles down leaving that nasty brown stuff in my fermenter. I was thinking about trying a 5 gal. w/ a 1" blowoff tube stuck directly in the top of the carboy as my primary next time. This would leave very little head space so the krausen would escape out the blowoff tube which would be a good thing for my beer, right? I haven't heard of anyone else doing this but it seemed like a good idea to me. Any thoughts?

Papazian claims that blowing off gets a bunch of yucky tannins etc out of the beer. I dunno. When I transfer out of my primary bucket, lots of gunk is left behind. All you can do is try the blow-off, and see if you think your beer is better or what....

I don't think I'd worry about the brown stuff on the side of the carboy. Once I used a 5 gallon for secondary fermentation for my blueberry wheat and it bubbled out of the carboy. Even then, a lot of brown residule was left behind. I think it is the tannins that are not released w/ the co2 that would be the biggest concern. The brown stuff left hanging out on the sides of the glass shouldn't pose a big threat to off-tastes.

I think you're cool with your 6.5 - but if you want to see if there is any difference- do what Sasquatch said: try it. That's what blow off tubes are for