Sic,
I don't see alot of responses that address the differences in the 2 cams you asked about and I think its because they are likely very similar and so it probably boils down to either your preference of the shop wrench's. I am no expert on this topic but I too went through a long period of trying to get the right cam to unlock even more power. Should I get .585 or .600 or .640? Back and forth, reading every post and thread i could find. Being on the back side of choosing an S&S .660 installation, let me share what I've figured out.
1. S&S is an awesome product, great engine work with lots of history of performance and reliability and also a stand up company that stands behind their product.
2. That after you make the change out there will still be loads of fine tuning to optimize the upgraded cam. Which is expensive and dangerous if you aren't living next to John Sachs or Will Weldon, or you're a fairly good mechanic yourself.
3. Upgrading the cam means more necessary maintenance and care since it's gonna increase wear on the motor more so than the stock cam would've.
4. The cam upgrade also adds expenses like less milage, increased tire turnover (Avon cobras excluded since they turn over too often regardless), and in my case increased starter work load making the need to upgrade it.
5. Lastly these bikes are pretty bad ass right out of the factory and smoke most other bikes on the road (crotch rockets and BMW touring bikes excluded).
So be sure this is what you want, and if experience is a good guide just ask Raywood about all the engine upgrades he has done, because I am pretty sure he is still running the stock cam with enough miles on that thing to circle the globe or something like that.
With all the above perspective I do have to admit that I love cracking my throttle and shooting like a bullet down the road while trying to hold on to my bike, it is just way more headaches for those rare opportunities to ride really aggressively. Good luck.