I have been keeping an eye on this release for the "rare and highest valued thread". It safe to assume that there is no shortage of demand. I would value the maximum value on eBay at about $1500 USD or about €1100.
But to get this it would have to be ultra mint (pun unintended), i.e. it not only needs to be sealed with no rips to the seal but must also not have any scratches or other faults to it which would not normally be considered an issue with a sealed game. This is to enable the buyer to grade the game at VGA and to get a high 90+ game. In other words copies still in there factory bubble wrap and original factory box from EA are considered slightly more desirable for this exact reason.
There are also cases where fully sealed game have gone for just $900,
http://cgi.ebay.com/Dead-Space-Ultra...ht_1880wt_1139
Of course any given seller may be ok with their copy going for this price, it also conceivable that there is a fault to the seal which the seller did not list.
I would say your asking price of €1000 is close but a little high.
I would value it between €850 - €950 Euro depending on the condition, but judging by the pictures you have supplied, it looks to be at the higher end of the scale.
Good luck with the sale, it's a fantastic piece to add to anyone's collection, surprised you even selling it.