An update on this issue. The 5 ore green stamp shown above exists with the KPV watermark. The Facit catalogue number for this variety is 79Bz. It's not particularly valuable - indeed one website is selling a mint strip of 5 for $42.
An image of the KPV watermark can be viewed here:
http://www.sfu.se/skola.php?edit=1&id=18&page=1My stamp (reverse shown above) has the KPV watermark reversed, in other words, reading the way it should from the front. I haven't yet been able to establish whether this variety has been listed or what it's worth.
The stamp is also known with crown + KPV (Facit# 75vm3). However, this is extremely rare and apparently only one used example has as yet been discovered. As is the usual practice with catalogues when dealing with items of which very few examples are known, Facit does not give a price for such a stamp.
A seller from Iceland recently listed the 10 ore stamp from the same series with crown + KPV watermark for $2,495:
http://cgi.ebay.com/Sweden-RARE-Wat...em4cf4c17e22