No, I haven't done serious testing and, if you read my posts carefully, you'll see that I've left the possibility open.
However, the claim that Rafal refers to and that you reference above is found ONLY in the Ilford data sheet on processing black-and-white materials ( http://www.ilfordphoto.com/Webfiles/200621111117720.pdf ). Such a claim is NOT found in either the data sheet for Ilford Rapid Fix or Ilford Hypam.
Because this issue is central to this thread, I contacted Simon Galley and asked him whether the information in this data sheet is still valid, i.e. whether use of a hypo clearing bath indeed allows four times higher reuse of single bath fixer. Here is his response (reposted with his explicit permission):
Originally Posted by Simon R Galley
Our technical service stand by the statements, they have been verified and checked over many years.
Simon ILFORD Photo / HARMAN technology Limited
Trying to be the best of whatever I am, even if what I am is no good.