I hope I didn't miss the boat here. I went on this same quest a few years ago. I tried a lot of .40-caliber handguns. Hands down, my favorite was the Beretta PX4. Despite having a polymer frame, it was both the most comfortable to shoot and the easiest for me to shoot accurately at speed. The rotating barrel system seems to have a lot to do with that. Capacity is 14, which is good for .40 S&W. I greatly preferred the stock DA/SA trigger of the PX4 to the P30.
Not everyone likes the batwing safety levers on the PX4. Beretta makes a kit to convert them to flush-fitting decockers. Doing that makes a huge difference in perceived width. It really helps to give it an edge for when you want to carry a full-sized forty. You should be able to get both the kit and the gun for under your $600 limit, with a little extra to put towards extra magazines.