I went from a RS6 to a 5BW. Initial reason for the RS6 is that the wife was pushy at the time about my second car being an auto, my daily is a mt taco
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If I only had room for one car, the RS6 would win since I live on LI and the awd would be nice in the winter, and the amount of storage in the RS6 is amazing. You can fit a ton of stuff in the back being that it's a wagon. The interior in the RS6 is better than the 5BW, but it is a lot of gimmicky things which contribute, such as the ambient lighting. 5BW HVAC controls are far better though instead of the stupid touchscreen which you need to glance at to make sure you're tapping the right icon.
Driving characteristics they are two different animals. The RS6 not only having more heft, has the entire engine in front of the front axle. You definitely feel the location of that mass when you toss it into a corner. It feels like it takes a second for the weight to load up the front wheels and then the turn in starts. Pure grip once in a turn on the RS6 was comparable, if not maybe a touch better than the 5BW, but it's not nearly as agile feeling. Turn in on the 5BW for a sedan is significantly more immediate.
The big difference between the two is the feedback from the car. The 5BW gives you queues the rear is working. It's far more engaging and rewarding. I also never had a pucker moment in the RS6, where the immediate torque and rwd of the 5BW will definitely let you get more rowdy. Nothing like breaking the tires loose in 2nd on the 5BW when you want to have some fun. I also thoroughly enjoy the 6mt in the 5BW. It has so much torque you can just throw it in 4th and put around town without needing to change gears if you're lazy. If you want to have fun the ratios are close enough that you can spend plenty of time rowing the gears if you want to. It's also extremely rewarding nailing a no-lift shift and leaving some schmuck in a 911 with bad hair plugs in the dust.