hey gutpile (clever name), i think i can answer some of that.
about reliability, the 4.0 will run forever if you treat it right, but thats true about most newer engines. how reliability compares to the 4-banger, i dont know, never having owned one.
you're right about having more power. from the factory, that 4.0 has about 195 HP, but theres plenty you can do to increase that. most of the jeeps in your area have the 4-cyl. engine, as you said, and... well... thats why its for sale! its worth looking around a bit to find a 4.0 one.
the 4.0 is made by chrysler, as far as i know, while the 4-banger is a GM engine, also seen in some passenger cars, like cavalier, grand am, etc., but also seen in trucks, such as the S-10's , and such.
its worth the extra few bucks and research time to get a 4.0
Dan, San Bernardino, California
'86 XJ, 2.8 V6 5 spd, 3" lift
"It may be a piece of sh**, but its MY piece of sh**!" -Me