FWIW, when cutting hardwoods, most people don't run their chains any more than 2 tanks of fuel meaning that after the 2nd tank of fuel the either the chain gets sharpened or gets swapped out for another sharp chain. Some of us even sharpen after every tank of fuel. If your chain is dulling faster than that, then (as others have mentioned) you're getting into some dirt. Either you're letting the tip touch the ground, or there's dirt embedded in or under the bark. This happens a lot if you're cutting logs that have been skidded/drug out of the woods.
As far as bigger saws and bigger bars, how big are the trees you think you will be cutting? If you provide as much information as possible, the folks on here will usually give really good advice on saws that will fit your application. The MS400 that was mentioned is a good saw that has an excellent power/weight ratio, but it's not been on the market very long. Finding a used one that's in good shape will likely be difficult. I don't have any history with Husqvarna saws so I can't make any recommendations there. They make great equipment, but all of my stuff has been Stihl. On the Stihl products, the newest models (MS400, MS462) lighter than than previous models of similar power. Spending more for the newer model may be harder on your wallet, but you're getting something in return. Whether or not its worth the extra cost to you is a different story.