I'm one of three or four people on the Panamera Board that decided on the GTS instead of the new M5. AND, we're all former E60 M5 owners. This tells me that a number of well informed BMW people have made the decision to purchase the GTS instead of the F10 M5. I gave up my 'first in line' spot at the dealer. I do think these cars are real competitors because: 1. Their pricing is similar. Yes, the GTS is some $15K more, but it's in the 'buyers range' for a car like this. 2. Yes, the M5 will blow the panny away in a straight line test. But I think the panny will hold it's own on the track. Sport Auto had a 1:13.5 time in sub-freezing temperatures vs a 1:12.9 time for the M5 in ideal conditions. I'll bet their track times are very similar, and that means the GTS must handle way better, given the 130HP deficit it's making up. 3. Yes, some say the panny is ugly, and the M5 is definitely better looking from most angles. But at least the panny looks like a 4-door $100K super car. The M5 looks like a tricked out 5-series, and might just be too 'subtle'. 4. The interior of the Panny is one of the best of any car available. The bimmer is better than the E60, but doesn't measure up to the panny. 5. The M5 has the most ridiculous feature of any car in the last 20 years - PRE RECORDED PIPED IN EXHAUST SOUND, because the natural engine noise doesn't get through the cabin. The panny has both the 'sport exhaust' and the 'sound symposer' - fantastic solutions to having a quiet car when you want it, but having a sports sound when you want that. 6. The panny is AWD. Big advantage in the snow belt, and a much more practical car for driving long-distances when you don't know what the weather will be. So, I think the GTS is the better car.