The 300-6 is a very good motor. I have overheated mine so bad you could feel the block shaking from the boil when I shut it down. I let it cool and it is still running. That is not something I am proud of, but when you have to dig through 3 feet of wet heavy snow with a load of wood and you will freeze in if you stop, you keep going.
These motors are bullet proof. My two brothers have them and I have one. They all work hard. I have hauled well over a million pounds in my f250 in the last 2-3 years. It still goes down the highway fine and gets about 18-20 mpg doing it. It will carry 9,000 lbs on the bed and goes anywhere. It is 2wd, but I have some meaty spike chains that provide plenty of traction.:hmm3grin2orange:
I try to stay away from the v8's because they don't seem to have the low end grunt that the 300 has. A 300 can also be built up to 300 hp and 400 ft/lbs on a budget. THAT is pulling power. I don't know what mine has in it for replacement parts because I have not opened it yet, but it has a TON of torque from 800-1400 rpm. My brothers can wind theirs out and have a full band. I used to be able to roll the tire through 4th gear but now I have armored tires to prevent punctures from stems/sticks and small diameter(1/2-3") stumps cut at sharp angles(thanks dad) and they weigh a TON. Big brakes are a must for a wood hauler since you can easily weigh 14,000 lbs in a loaded 3/4 ton.
I would pass on both. Automatics and v8's have a place, but not hauling wood. I recommend something with an inline engine and a manual transmission. 4wd is not a must, but is handy, and is more maintenance. You have to use it or it will go to pieces. The reason you don't see medium or heavy duty trucks with v8's is because they lack torque, are less efficient, and are harder to work on. An inline engine gives very good torque because the cylinders are not offset. A V makes hp and a straight makes torque. Torque is how much work you can do and hp is how fast you can do it. My brother's big truck has 400 hp but 1200 ft/lbs of torque and is an inline. It works very well as a stump puller or chain/strap breaker.
This is just my observation in a tired state. Please forgive any ramblings or other imperfections.