That last one doesn't appear to have a fan. For general or HTPC use, it would be great. For gaming, it might overheat unless you have really good airflow through your case.
The HD6670 is the strongest of the cards you've listed (in some cases by a lot), but if you can, get a GDDR5 version rather than DDR3.
If you want to play ARMA2 without any hiccupts or problems I recommend a used 5770 from ebay, wont cost u 50 quid for a decent deal. ELse u can add around £20 and get a HD 7770. In my opinion itis worth the extra 20quid on top.
CUrrently a HD 7770 fetches for around £80-90, but you should tell u more about your system before upgrading just incase there are other issues.