No, the 60lb valve springs don't hurt anything. If you ever put an exhaust brake on it, you should put in the heavier exhaust springs anyway. As far as the throttle being touchy, it can be, if the springs aren't adjusted right. I tried both, the 3K and 4K. I didn't notice too much difference in them, but with 4. 10's, I would go with the 4K.
Jim