It does. Last year I got a bag of Crisp #19 floor malted maris otter. The first beer I brewed with it was a bitter that came out great and it had an 8 point higher original gravity than the previous version of the recipe using non floor malted m o.
Michigan hop allience went above and beyond what could be expected. Even though I wasn't an actual customer and they wasn't responsible for the repackaged samples I received they sent me some cashmere hops free of charge. They smelled heavenly.
You won't get much effect on flavor using only 5%. The closest that I ever got to the sour tanginess of Guinness was when I cold steeped the roast barley overnight, but left it out at room temperature instead of putting it into the fridge.