New 6.1L hemi's is anyone using them?

Hey guys, seen a few more 6.1L hemi's pop up on ebay of late. Just wondering if anyone had bought one and I have a few questions as well.

With the 6.1L's out of factory cars i.e. 300c, chargers, jeeps. I read on one ebay ad that they have some sort of code so that they can't be used once they are wrecked (or something along those lines), do they just need to be reprogrammed? Or need a new computer?

Factory Jeep 6.1L

These ones are going for around start at low $6500 buy it now for $8,400 motor only. Then I see other ones like this:

6.1 Factory block 0 miles
with buy it now of $5,850, is there any actual difference between the two engines??? It's apparently from the factory and you need to buy an additional computer, but would that engine perform any different to the one from factory cars in way of reliability, drive ability, or fuel economy etc????

I guess the same question goes for the 5.7L engines from ram's and 300c's do the 5.7L fuel injected crate motors perform any differently?

Still undecided on which engine to go and whether to go crate or wreck.

Hope this makes sense. Cheers Dave.