The A8 is luxury car and is something you would generally buy if comfort and luxury is on top of priority list. So, L 3.0 TFSI variant justifies the cost and features on offer. It also gets all the amenities and luxury features that the pricier L 4.0 TFSI Sport variant gets. Moreover, paying $9000 more for a slightly more powerful engine doesn't really make sense and so the L 3.0 TFSI variant is just the one you should buy.