i've heard it is 4000-5000km but i'm not sure what I should take seriously.

Not too far to the right, because then it'd be nazi

The word you are looking for is probably "east".

For geographic discussions you should look at http://www.gamesas.com/topic/1477655-musings-on-the-scale-of-tamriel/ http://www.gamesas.com/topic/1504420-musings-on-the-scale-of-tamriel-ii/.

Much of it is well founded speculation. Exact numbers are hard to come by.