All the cars you listed are really good. Picking a sports car is a really personal choice. I've test driven all of them. I'm a little late to replying to this forum, but if you're still looking, you should know that the S2000 is a fantastic handling car. If you don't have the roads to rev the engine, it will feel underpowered. (my review)^Good points, all of them. You and a few others have all but convinced me that I will have more use and my family will have more fun if I get a nice sports sedan like the M3 that the whole family can enjoy together. It WOULD be fun to roll up to a cars and coffee with everyone in tow rather than having us all take different cars. I'm not abandoning the thought of getting a CS, but it is slowly but surely moving into a plan-B rather than plan-A.
If you want something that works more like a daily driver (with usable torque), you should definitely consider the M3. In order to get power from a Cayman S or a 997, you need to get it above 3-4k RPM. In the M3, torque is delivered lower, which gives it a nice pull. Overall, M3's are really balanced cars. It rides like a sedan, but handles really well. You kind of get two cars in one. If you like that idea, I'd recommend selling off your daily driver and get a 4 door version of the M3. It does everything *really* well... except turn heads. (my review of an older m3)
A Cayman S, on the other hand is a much firmer ride. I could see it getting exhausting for some people. It shares a lot of similarities with the S2000 in terms of handling. The Cayman S is a very capable car, and if you plan to go to a track, you'll have a lot of fun. It, however, doesn't have the same heritage as the 911... which is the heart and soul of Porsche. (my review)
So that leaves the 911. If you're looking at the 997, I can tell you that it's phenomenal—I own one. It takes a lot of motivation to drive it. It's a unique setup—rear engine, rear wheel drive... so you have to really know how to balance the car's weight distribution when driving at the limit. There's a challenge to driving an 911, but with that challenge comes great reward. It's not the fastest car, but it is really fun to drive... and there's a really huge following around it too.
Anyway, from the sound of it, I'd guess that you're looking for some more usable torque. Test drive all of them, because they're all very different. The Cayman S will be the closest to the S2000 in terms of handling. The M3 will deliver usable torque and has a very compliant ride. The 911 will get give you more challenge and reward in the long term.
That being said, if you're a serious torque or G junkie, you may want to consider an older GTR or 996 turbo. You can probably pick them up for $45k as well. Hope that helps! Good luck buddy!