Hi soren40, welcome to the forum.
It is a bit quiet on here at the moment, many owner put the Xfire to bed for the winter
Well I own 3! SRT-6 Coupe, SRT-6 Roadster and a Limited Coupe
The choices you have are quite simple,
Limited or N/A are available in Coupe and Roadster, Manual and Auto 3.2 V6 215 Bhp
SRT-6 in Coupe or Roadster only Auto with an AMG 3.2 supercharged V6 350 Bhp. the spec say 330 but AMG never produced any engines at the power
They are all pretty bulletproof, parts can be hard to find, but not impossible and can be quite pricey.
You will struggle to find an SRT-6 as there are only approx. 100 in the UK and they don't come up for sale very often but if you can find one, it is the one to have.
I have no idea what the MPG is as I don't care
with your 6k budget you should find a good N/a, buy with your head not your heart. not any Chrysler dealers anymore so see where it has been serviced, loads of stamps in the book are useless without the invoices to back them up. Most important make sure only Mobil1 or equivalent engine oil has been used.
All in all there isn't really anything to particularly to look out for other than the obvious when buying any used car.
good luck with your search, keep us informed.
Mo