Just like "Das Boot" you want to go with the long version of Talvisota which is over 3 hours. The character introduction/developement is much better in the long version. There is also a TV Version which is over 4 hours long, but I am not sure if you can get it with subtitles.
I have a copy of "Tali-Ihantala 1944" here, still haven't watched it though. The film didn't have a big budget, however it looks quite decent, it seems that the filmmakers valued authenticity:
http://en.wikipedia.org/wiki/Tali-Ihantala_1944 (you can find a link to the movie site at the end of the article)
Plus you can get it for a bargain price here, I paid roundabout 5 Euros for it

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