I recently kegged a 9.7% abv Belgian Tripel that was in a 10 gallon Rye Whiskey barrel for 2 months (which was almost too long). It came out really nice. I used my barrel rinser to rinse out some of the Whiskey flavor before transferring the beer into the barrel. The oak, Belgian esters, Pilsner malt and noble hops really blended well. The reaction people have when they smell it initially, without being told it's barrel aged is priceless. It's hard to stop drinking it.
Fermenting: Azacca Oat Pilsner, Egregious-ish, Barrel Fermented Dreg DelcoLambic, Sacch Trois Helles
Drinking: RIS v7, Doppelbock, RIS v6, Carrot Blossom Cedar Mead, Sauerkraut Fermented Gose, Gueuze, Brett Blonde, Kriek, Saison, Sour Blonde
Barrel aged: Rye Barleywine, Tripel, Wee-Heavy