A 30 deg rating is not an excessively warm bag, you just might be glad to have it at higher elevations. If you feel too warm, unzip the bag and use it as a blanket.

Down bags are nice because they're very comfortable, very lightweight for the insulation they offer, and they stuff down to a very compact package. On the debit side, they lose all insulating value when they get wet and they are hard to clean without destroying the down. They also should be stored fluffed up, leaving them compressed in a stuff sack for too long will wreck the down. I use a silk liner at all times in my down bag, I'm obsessive about storing them unstuffed when I'm not on a trip, and I get 15-20 years from a bag. I also am very careful about packing the bag in a good waterproof stuff sack when I'm on a trip.

If you have the money and are willing to take care of your bag, down bags are the way to go. If you expect to be in a situation where it will be impossible to keep things dry, consider synthetics.

I've found Marmot and Western Mountaineering to make excellent sleeping bags, and I've heard good things about Feathered Friends. None of these brands have ever been called cheap, but they make high quality products that will give a lot of use and satisfaction for a long time.