Go with the 4.0. The 2.5 is a turd and it's not much better on gas if at all. The 4.0 is more easily modded. The 2.5 is just ok off road and even then, you will definitely want to re gear if you go any bigger with tires. In my opinion, the only thing the 2.5 will do for you is save a bit of money on the purchase price.
"It's all good. We've caught a lot nicer shit than this on fire"