I currently have both a 997.2 GT3 and an ESS 625 E90 M3.
If I had to DD the GT3 I would end up disliking it and selling it. I drive it to work every once in a while when I really feel up to it. But it would get tolling everyday. The GT3 makes the M3 feel like a lexus in traffic, but the GT3 is such a rewarding drive. It has a great feel, even in a straight line but I prefer it in shorter stints, where the M3 is great for all times but doesn't feel nearly as special.