Just wanted to report that I've had a fair amount of success with the method described in the last post.
Here's what I did.
(suppose project is named "MyProject")
1. From within soapUI in MyProject I created a new Test Step inside my test. I named the new Test Step : "LargeRequest". The only thing I put inside the request was the text "BlaBlaBla". I then closed soapUI again.
2. I then I copied soapUI project file from MyProject.xml to MyProject.txt. (I do this solely to avoid that my text editor, I use Notepad++, will try to interpret the file as XML, which it freezes on because of the size).
3. I then use my favorite text editor, in this case Notepad ++, to open file MyProject.txt. I then find the text "BlaBlaBla" and on that spot in the file I insert the contents of my large XML request (which I have in a another file). The request needs to be in a CDATA enclosure:
<![CDATA[your-custom-xml-here]]>
I then save the file and rename it back to MyProject.xml.
4. Now I open soapUI again. As it turns out I can actually open the Test Request "LargeRequest" in the soapUI editor without problems and I can put assertions on it.
Bingo!
If you don't use the above method then the only method to get XML into a request is to
paste it from the clipboard. My guess is that it is at this point where soapUI freezes. Pasting into the editor was how I started out and that is what made soapUI freeze.
I'm still struggling to get soapUI not to freeze when it receives the response. The response is roughly 50 Mbytes due to the verbosity of XML. It isn't really a lot of real data, it is just that XML is so incredible verbose. I'll let you know how I get along.