660Sm is ok with more comp , and you would want to swap springs in my opinion .. But it does work well .. Before going through the list , what are you trying to obtain
I love the low end, and I'd like to keep as much as possible. However I go out and ride solo somewhat aggressively more than I take long trips with groups. I'm not taching out every second, but ride a little higher in the RPM range more than the average rider. It's tough, because it's also nice to hit the throttle at 2500RPM and have that instant torque. Maybe in a perfect world I could have both

I would like to find something that is a bolt in cam, something that runs "safely" with the stock set up that broadens the TQ curve. Would like to avoid getting into the heads and all that.
Would it help if I found some examples of dyno graphs that showed what I would like to achieve? I hope what I posted helps some, and thank you all for your suggestions.
EDIT: Dyno chart on the 600SM's looks nice. That cam is ok with a little less than the recommended 10.1-10.5 compression?
GMR - It looks like your 577 cam runs nice, too. Seeing lots of charts getting 100TQ before 2500, and still keeping 100 TQ to 5500 or so. May throw that into consideration as well!