Preheat oven to 400°F. Fill a large stock pot with salted water and place on the stovetop over high heat. Bring the water to a boil and add the dried macaroni. Cook the pasta according to the package directions until just shy of al dente. Drain the pasta in a colander and set aside.
In a large sauce pot, melt the butter over medium heat. Add the flour and whisk until smooth and bubbly. Slowly pour in the milk a little at a time while continuing to whisk. Repeat until all the milk has been added and the ingredients are blended and smooth. Continue to simmer for three to four minutes, whisking occasionally until the sauce thickens. Stir in the shredded Cheddar and Jack, cream cheese, salt & pepper, garlic powder and paprika. Continue to stir until all the cheeses are melted and thoroughly incorporated. Stir in the macaroni and the sliced pimientos and mix well.
Transfer the macaroni mixture into a greased 13x9-inch casserole dish and place into the oven uncovered. Bake for 20 to 25 minutes or until the cheese is bubbly and the edges have browned. Remove from the oven and let stand for five to ten minutes to allow the cheese to thicken before serving.
