Congratulation on your new 528i. Very nice.
I'm going through the same process of trying to choose between the A6 and the 5 series but I'm also considering the 535i to make things even more confusing.
Since I'm going to be ordering a 2013 I have all the time I need to make a decision. I keep waffling back and forth between the Audi and BMW as both have there strengths and weaknesses. So far I've been able to get two shorter test drives in the A6 and a couple of shorter and last weekend and fairly long test drives in both a 528i and 535i. But the Audi dealership keeps the cars unlocked when they are closed so I have been able to get ample static seat time in the A6. If everything was equal, I would probably have chosen the 535i but it comes in way higher than the 528 and A6.
It's good to hear I'm not the only one thrilled with seats in the A6. Although the ventilated ones in the Prestige model are better they still don't blow me away and are not as comfy as the seats in my M35. I think Audi is missing the boat here and loosing sales by not making their sports seats an option in North America. The multi-contour seats on the other hand are just this side of heaven and fit like a glove. Although the seats in the Audi are not uncomfortable there is no comparison the the multi-contour seats. Major advantage BMW.
I've seen some criticisms of the 5 series for being too conservative but I like the exterior of the 5 series better and strangely enough I like the interior better also. The exterior of the 5'er is just classy in my book. The A6 is also nice looking but I prefer the 5'er. The interior of the A6 is beautiful and functional at the same time while the 5 series seems much more business like and plain. I'm not a fan of the motorized MMI screen in the Audi at all. But one thing I immediately notice between the two is the craftsmanship and built quality of the BMW is head and shoulders above the Audi. Although both have excellent fit and finish, the materials, textures and solid feel of the 5'er makes it a place I want to be. The A6 has a somewhat cheaper feel to me. Not nearly as solid and luxurious as the 528/535. Some of the surfaces have a "hollow" feel/sound that I haven't noticed in the 5 series. I do like the information area Audi has between the speedo and tach. Lots of info can be controlled from the steering wheel and displayed there.
Audi has the advantage of raw power and immediate throttle response. I've been nothing but impressed with the 3.0t engine mated to the 8 speed ZF. The 528 is certainly adequate and the 535 closer to the A6 in addition to silky smoothness and wonderful mechanical sounds. In day-to-day commuting any of the power-trains would enough. Both BMW mills are more fuel efficient than the Audi although all are better than my current Infiniti.
Even though they are pretty close to the same weight the Audi feels and drives like a lighter car. The 5'er feels heavier but this pays dividends on the highway. From the limited seat time I've had the A6 would seem to be a more fun to drive car. The 5 series is a better/quieter cruiser on the open road. If I cut up the back roads a lot this would be more of a downside but the cold, hard facts are I spend most of the time in my car commuting on the freeway
The all wheel drive would be wonderful if I lived somewhere it snowed (or even rained) but since it is sunny and dry 99% of time around here AWD isn't a big deal to me. I haven't driven a non-sport 5'er but everything I've read leads me to believe it is a mandatory option for a 5 series while the A6 seems to get along better with the base setup.
The Bose setup in the A6 Prestige model isn't anything special IMHO. The reasonably priced Premium Sound Package in the 5 is better. My BMW dealer was very accommodating in parking two 5 series next to each other and letting me hop back and forth between the two to compare the base/premium sound packages. A nice touch. The B&O in the Audi may be like being in a concert hall but I'll never know because I won't pay $5,900 for an upgraded sound system in a car.
A couple things that concern me about the 5 series is the fact BMW forces us to accept RFT. I've heard nothing but bad things about them and the cost to replace the tires (especially in the sizes that come with the M-sport/535i sport package) is scary considering the very short tread life. What kind of tread life can I expect out of the M-sport RFT? I would hope to get 10k miles out of them since I'm not a particularly aggressive driver (if they don't destroy themselves first). Still $1,500-$2,000 a year in tires is probably a deal breaker for me. There seem to be lots of little and small issues which I'm not sure have been resolved like the HPFP, throttle delay, bent rims, flat tires, vibrations, pulling to the right etc.
I still haven't made up my mind. I'm leaning toward the 5 series but when I price the cars out I can get the A6 for several thousand less than the BMW. If money were no issue it would be an easy dissension but $60k is right at the max I'm willing to spend and the A6 come in significantly lower than this pretty much loaded with everything I want while I have a hard time getting a 535i to come in at this price after I option it the way I want it.
Decisions, decisions.