40hp is huge! That is a 20% increase, and you would defiantly feel that...100hp, no way, I really cant see that. In mustang speak, the stock 5.0l had 215hp, and a 20 hp intake had a real big increase from the seat of the pants feel..
The advertised numbers are misleading on any "power adder". Ideally, you want to see a dyno graph of your combo (stock in your case) vs the addon(s) you want and the post install dyno thrash. 26 hp is great, but not at 4600rpm unless that is the engine speed where you drive.
Coming from a world of mustangs, exhaust is great to start with, then a free-er breathing intake, followed by some nicely port and polished heads and a cam. you will wake that engine/Jeep up.
The question really is, how much do you want to spend? And, how much time can you have it down? I ask this because these 4.0l are pretty relaible, and in my experience with my mustangs, the more power added via aftermarket, the more headaches and $$$ spent to keep it working right.