Joecarve:
YES. Definitely take the +1 approach to those spring rates. I'm using my board strictly for carving full 'C' type turns, slalom turns, and everything in between, and with the yellows the board is way too loose. There is one benefit: Balance will be improved! I have the tension on the yellows maxed out.
Hopefully today, two pair of purple springs will be arriving at my door. It's two steps up from yellow, but I put a lot of power into my carves, so I'm looking for more resistance.
My trucks are at 45 degrees front and rear, and this setup is great. I have not tried different spring rates yet, though I do prefer to have the rear tigher than the front.
BTW: I got my siesmics and my wheels from Gary at Asphaltplayground.com
He's very helpful, and will answer any questions you can come up with. He recommends 45 degrees up front, and 30 in the rear, but I don't think you'll get the carving effect you are looking for with that setup.
Tell him Tom Williams sent you! ;)