I'm hardly an expert (I just bought my first Porsche, a 2000 Boxster S, 48 hours ago!) but I decided to for once do some research on buying cars before I drove by a dealer with my wife and go OHHH lets get that one!!!
I know I've been screwed in the past but I felt better after doing a lot of research on the web, starting with :
http://www.carbuyingtips.com/
Theres a LOT to read there and many references to other sites to figure out what cars are worth, how to negotiate, not dealing with MSRP and making an offer based on what options you get, etc. Not sure how much applies to the more luxury oriented market but I found it all a good read.
As for the seat, I drove probably 10 cars before I settled on the perfect one and in that time learned so much about operating all the equipment... it took 5 cars to figure out the seats!! I'm 6 foot too and found the car really cramped at first but I finally got the manual seats to go all the way down and it was so much better... are you sure you have the older models all adjusted right? Just a thought.
Good luck