Allright, my promised update: My Ram finally arrived and I happily put in the 8gb and… It went all south. Horrible boot time, bad performance the whole 9yards. Bios (thank you HP) didn’t even let me change the clockspeed of my ram. Anyways since I wanted to give my Wifes Laptop (her active one) an upgrade anyway I got the 8gb ram in her machine and that one works like a charm (-windows). So I had 4 gb left now (from her machine). Well, I stuck that one in this linux machine and they now play nicely.
So all in all a great success story! Thank you for encouraging me to upgrade it!