I've owned several cjs 4, 6, and 8 cylinders all have been daily drivers and this is what i can tell you from experience.
my first jeep cj7 4cyl with 33s = no power, slow on incline on highways.
second jeep cj7 8 cyl 360 with 33s= lots of power and nice sound but 15 gallon tank will be empty at about 100 miles or so. It was bad on the wallet, someone here said get a 20 gallond tank i will agree.
third jeep cj7 6cyl 258 with 33s= best of both worlds good in gas and plenty of power for what i need as daily driver and occasional trail riding. But i do
miss the sound of that 360, and i've been thinking in installing a 40 series flowmaster which it will make my 258 sound alittle better but never quite like the 360. good luck.
Im thinking about a ford 351 windsor for mine.. I feel like the 258 is underpowered .. I even had a dream about it last night (call it an addiction!!) the 360's oiling problem... i didnt want to deal with that.. I know that the value will be lowered but I think ill take the ford.. :P
Go for it! You will not be disappointed.
All that about 6's is great until you drive it with an 8 in it!
You may pay a little more in gas or you may not.
I'm getting 16+MPG. That's with a correctly programmed speedo.
I'm running 32's and 4.10 gears with a TBI 350.
Swap in an OBDI 4.0l HO from an XJ. It will give you 6 cylinder longevity and "economy" and be an easier swap. It will have more power than you need to run on the highway and it is only really an upgrade, not a swap.
V8s are great but as a DD do you really want that level of cost?
My 258 is a daily driver and is surprisingly reliable for a 30 year old vehicle. The economy is probably not great but at 40c a litre I do not mind.